Portabella Mushroom & Vidalia Onion Gratin

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We love mushrooms alongside steaks at our house.  Most often I saute them with minced garlic, onions, balsamic vinegar, rosemary or whatever other seasonings my heart desires.  But, this dish, is a nice way to change up one of our favorite accompaniments.  Onions are in such abundance in the Summer months, and the flavors in this dish are only heightened by the sweetness of the onions.  Creamy, cheesy mushrooms and sweet vidalia onions are topped with a crispy homemade crumb topping, then baked until bubbly.  I often serve this on the side, but, you could also serve this as a topping for a baked potato, over egg noodles or buttered rice.  Try spooning this gratin over a piece of grilled chicken...oh my,  heavenly!


You'll need:

1 pound of sliced baby portabella mushrooms
1 x-large vidalia onion sliced into small wedges [or 2 medium]
2 cups of shredded muenster cheese
1 1/2 cups of milk
3 cloves of minced garlic
3 Tbs. butter divided
3 finely chopped green onions
2 Tbs. chopped Italian parsley divided
2 1/2 Tbs. all purpose flour
1 Tbs. red wine vinegar
2 tsp. fresh thyme
salt & pepper to taste

For the crumb topping:

1 1/2 cups of fresh bread crumbs
1 Tbs. chopped Italian parsley
1 Tbs. melted butter
1/4 tsp. garlic salt


Preheat the oven to 350 degrees and butter a 1 1/2 quart baking dish, then set aside.  In a heavy saucepan, saute the mushrooms and sliced onions in a couple of drizzles of olive olive until the mushrooms are golden and they've released their liquid.  Season with salt and pepper to taste.  This step will take around 12-15 minutes.


To the mushrooms, add the minced garlic, fresh thyme, 3 tablespoons of butter, 1 tablespoon of red wine vinegar and 3 chopped green onions.  Continue to saute over medium heat for 2-3 minutes until the garlic has cooked and the butter has melted.


Next, add 2 1/2 tablespoons of flour and cook for 1 minute until the flour has coated all of the ingredients.  Increase the heat to medium high and add 1 1/2 cups of milk.  Cook until the mixture is bubbly and has begun to thicken.  This will take 2-3 minutes.


Next add 1 1/2 cups of  shredded muenster cheese and 1 tablespoon of chopped Italian parsley to the creamy mushrooms.  Cook just until the cheese melts.


In a small bowl melt 1 tablespoon of butter in the microwave.  Toss the breadcrumbs, chopped Italian parsley and garlic salt with the melted butter to make the crumb topping.

Pour the mushrooms into the buttered baking dish and sprinkle the remaining shredded muenster cheese on top.  Spread the buttered crumbs evenly over the cheese.

 
Place into the oven and bake for 25-30 minutes until the topping is golden and the edges are bubbly.  Allow the gratin to sit on the counter for 5-10 minutes before serving to allow the sauce to thicken.  Yield: 8-10 servings 



Cook's note:
For this dish I purposely chose muenster cheese for it's saltiness.  Gruyere cheese also works beautifully in this dish!