Portobello Mushroom Gratin with Seared Foie Gras
1 lb portobello mushrooms, sliced thin
1/4 c. unsalted butter
1/4 c. all-purpose flour
2 large onions, sliced thin
8 - 10 T. heavy cream
1 c. grated gruyère cheese
1/4 c. fine breadcrumbs
½ lb foie gras
1 T. minced fresh thyme
Toasted rounds of baguette (to serve)
In a fry pan, cook the mushrooms in 2 1/2 tablespoons of the butter over moderately low heat, stirring, until they are softened and most of the released liquid has evaporated. Stir in the flour and cook, stirring, for 3 minutes.
Using eight 8-ounce or ten 6-ounce ramekins, depending on the number of people you are serving, layer the onions, the remaining butter (cut into bits), the mushroom mixture, and salt and pepper to taste, beginning and ending with a layer of onions. Pour 1 tablespoon of cream over top each ramekin. In a small bowl, combine the gruyère and breadcrumbs and sprinkle the mixture over the cream.
Preheat oven to 325°F. Bake on the middle rack for 50 to 60 minutes, or until onions are tender and the tops are golden. The gratins may be prepared 3 hours in advance, kept covered and chilled, then reheated in a 400°F oven for 5 minutes, or until they are heated through.
Just before serving, slice the foie gras into 1-inch thick pieces and sear it in a hot pan until golden brown on both sides. It will smoke, but that’s normal. Place a slice of the foie gras plus a small drizzle of the oil left in the pan on top of the gratins, then serve garnished with the fresh thyme. Serve with slices of toasted baguette on the side.
: Instead of placing the foie gras on the gratin, you can make “greasy toasts” to accompany the gratin on the side. Slice foie gras into ½“-thick rounds and place on top of the toasted rounds of baguette. Bake in a hot oven for a few minutes, then serve with gratin.