12 cremini or white mushroom caps, 2 to 3 inches wide
12 mushroom stems, minced
1 Tbsp butter
2 Tbsp olive oil, divided
1 tsp fresh rosemary, minced
2 clove garlic, chopped and separated
3 Tbsp onion, minced
3 Tbsp shallot, minced
1/4 cup Madeira
3 Tbsp bread crumbs (plus extra for topping)
1/4 cup Gruyere cheese, shredded
1/4 cup Parmesan cheese, shredded (plus extra for topping)
4 Tbsp parsley, minced
1/2 tsp tarragon
2 to 3 Tbsp heavy cream
Salt and pepper
Preheat oven to 350. Put the mushroom caps in a large bowl with 1 clove garlic, rosemary, and 1 Tbsp olive oil. Toss to combine. Arrange stem-side down on a cooling rack over a baking pan (so that the moisture will drain out as they cook). Bake for about 10 minutes, or until a paring knife feels a little resistance sliding in (not soggy, but not raw). (Don’t turn the oven off.)
In a pan, melt the butter and oil together. Add the onions and cook for 3 to 5 minutes, stirring quite frequently. Add the shallots and 1 clove garlic and continue cooking for another 1 to 2 minutes or until soft. Add the minced mushroom stems and continue cooking for another 10 minutes or so. Add the Madeira and simmer rapidly until almost totally evaporated.
Take the pan off the heat, and stir in the bread crumbs, Gruyere, Parmesan, parsley, tarragon, and salt and pepper to taste. Slowly mix in the cream until the mixture is moist but still holds together. Taste and adjust seasoning.
Try to dry the mushrooms as well as you can. Turn the mushrooms stem-side up and fill each with about a teaspoon of the mixture. Do not pack it in. Over top of the mixture, sprinkle some more bread crumbs and Parmesan.
Bake at 350 for 20 minutes, then turn on your broiler and let the tops of the mushrooms get browned. Best served hot.