Sweet Potato and Mushroom Casserole

I promised a side dish last time, and then I got to thinking that I hope that everyone is not tired of sweet potatoes, having just gotten through the holidays!  I am going to post it anyway, because it really is yummy.  It would be great as a side dish, or as a vegetarian main course.

This dish was inspired by a little hole-in-the-wall restaurant that used to be in downtown Salem called the Soup Cellar.  It was run by Marc, who made everything from scratch, right down to the salad dressings and sauces.  It was phenomenal food!  He operated there for several years before suffering burnout from the long hours and the high overhead cost of running a restaurant, and sold the establishment to someone else who could not hold a candle to the original, and soon went out of business.  I sure miss that place!  He had a few regular specials that he rotated on the menu, and one of them was a baked sweet potato, topped with sautéed mushrooms and onions, fresh chopped herbs, and his own yogurt-tahini sauce.  It took me awhile to work up the nerve to try it. Growing up, my experience with sweet potatoes was confined to the syrupy-sweet marshmallow-topped variety on the Thanksgiving table, which just never appealed to me.  I confessed my misgivings to Marc one day, and he assured me that I would like his sweet potato.  He was right- it was the perfect combination of sweet and savory.  I have since renounced my prejudice of sweet potatoes and have enjoyed them in a number of savory dishes, including this one, which is now a Thanksgiving staple at my house.  But the one I am sharing today, I think, has to be my favorite.

Now, I have baked sweet potatoes before and had them with the mushroom-onion sautee, and it's...fine.  It's never quite as good as Marc's was though.  One problem I have is that most of the sweet potatoes in my grocery store are way too large for a single serving.  They take a long time to bake, and then they are not practical for bringing to work for lunch because of their size.  What I wondered was if it would be possible to create a casserole dish that would incorporate these ingredients, and if it would be similar enough in flavor to the original.  I began to envision a casserole of layered thinly sliced sweet potato, baked until tender, topped with the mushroom and onion sautee.  But how to do this without drying out the sweet potato?  Perhaps a gratin?  or something along the lines of a skillet casserole, like a Pommes Anna, only with sweet potato instead of potato?  My research began.

First, I looked up sweet potato gratin recipes.  A gratin is basically a vegetable baked with a cream and/or cheese, which certainly is very flavorful, but not really what I was going for.  For one thing, I was looking to keep the fat content low for my dish, I didn't want anything saucy, and I also wanted the flavor of the sweet potatoes to be unchallenged by a sharp, tangy cheese sauce.  Next I looked at recipes for Potatoes Anna.  For this dish, thin slices of potato are layered with butter in an overlapping spiral in a skillet and cooked until the bottom slices form a crispy crust, while the slices above it cook through to become soft and tender.  Inverted onto a plate, it forms a lovely presentation, and the contrast of the crispy potato crust with the tender middle is enjoyable and delicious.  This method did solve the problem of cooking the sweet potato without the use of cream or a sauce, but again, not really what I was going for.

Still, I ran across this recipe from the New York Times for Sweet Potatoes Anna, and it looked promising.  Instead of being cooked on the stovetop in a skillet, the layered slices of sweet potato were tossed in melted butter and then layered in a round gratin dish, weighted down, and then baked at a high temperature.  Brilliant!  Tossing the sweet potato slices with melted butter keeps them from becoming dry while cooking, although it does add a lot of fat.  I thought that I could probably reduce the amount of butter and substitute with canola oil and achieve the same results.   So this recipe became the basis for my own, with some modifications, of course.  This recipe uses thyme, which reminded me of the fresh herbs that Marc used to sprinkle over the topped baked sweet potatoes, so I incorporated that into my recipe as well.

I should mention that my initial run of this dish was on quite a small scale.  Since I knew that I was the only one in my family who would eat this, I did not want to make a huge dish.  Do keep that in mind, and consider doubling or tripling the amounts to make a larger batch, as well as increasing the time in the oven.

This was a success for me- the flavor came very, very close to the memory of Marc's baked sweet potatoes.  Next time I will probably use more mushrooms and onions than I did this time.  The amount I had did cover the top of the casserole, but barely.  I think it would be better with a good inch layer of the mushroom/onion sautee.  The tahini sauce was ok, but was too thick, so I will be reworking this in the future.

Ingredients:

1 large sweet potato, peeled and sliced very thinly

2 tbsp. butter, melted

2 tbsp canola or other vegetable oil

Salt/pepper to taste

Thyme- a couple tsp fresh chopped, or couple dashes of dried

Mushrooms- about a dozen, washed and sliced.  I used regular white, but you could use a mix of different ones

1/2 of a large onion, diced

1 shallot, minced

2 cloves garlic, minced

1 tbsp canola or vegetable oil

1 tbsp butter

Salt/pepper to taste

Instructions:

1.  Preheat oven to 425 degrees.

2.  Place sweet potato slices in a large bowl and sprinkle with salt and pepper.  Add thyme, melted butter, and oil, and toss until slices are well coated and seasonings are distributed.

3.  Spray the bottom of a 9 inch round casserole, baking dish, or oven-proof skillet with cooking spray.  (I used a Pyrex deep-dish pie dish.)

4.  Place sweet potato slices around the outside of the bottom of the dish, slightly overlapping the slices to form a ring around the outer edge of the bottom of the dish.  Then make another ring just inside the first one, slightly overlapping the outer one.  Continue adding additional rings until you reach the center, so that you have one layer of sweet potato slices covering the bottom of the dish.  Repeat with a second layer on top of the first, until you have used all of the slices.

5.  Place a sheet of foil directly on top of the sweet potatoes.  Place a baking dish or skillet slightly smaller in diameter than the one the sweet potatoes are in on top of the foil, to weigh down the sweet potatoes.

6.  Place in preheated oven and bake for 15 minutes.  Check after 15 minutes.  Sweet potatoes should be tender but not mushy.  If still too firm, bake for another 5 minutes and check again.

7.  While sweet potatoes are baking, sautee mushrooms and onions.  Heat 1 tbsp canola oil over medium-high heat in a skillet.  When hot, add onions and reduce heat to medium.  Cook 5 minutes or until onions are translucent and tender, then add mushrooms, shallots and 1 tbsp. butter, mix to incorporate with onions, and distribute over the bottom of the pan.  Do not stir for at least 2 minutes.  (This is the secret to great sauteed mushrooms- leave them alone!)  After at least 2 minutes, stir a bit with a spatula and then let them be for another minute or so.  Mushrooms should brown before each stir.  Continue to cook until most of the liquid has evaporated and add garlic, thyme, salt and pepper.  Stir and cook 1 minute, then remove from heat.  Set aside.

8.  Remove weight and foil and place back into oven, uncovered, for 10 minutes.  Sweet potatoes should begin to caramelize on top.

9.  Remove mushroom mixture from skillet using a slotted spoon and spread on top of sweet potatoes, covering them completely.  Put casserole back into the oven for 8-10 minutes, until mushroom mixture begins to bubble.  Remove from oven and rest 10 minutes.

10.  Slice into wedges.  Serve with yogurt-tahini sauce (below) to drizzle on each serving.

Yogurt-Tahini Sauce

1 cup plain yogurt

2-3 tbsp tahini (taste as you go, adding more until the balance is right)

4 tbsp lemon juice

1 tbsp soy sauce

Whisk all ingredients together.  Can be served immediately, but it's better if it is made ahead.  Add more liquids (more lemon juice, or water) if necessary to thin, but be careful not to add too much soy sauce or it will be too salty.

I will be posting again soon with a favorite soup recipe.  I scored a great sale yesterday at the grocery store on bone-in chicken breast halves, and that means soup!  Check back later this weekend for that one!