Trim and halve green beans, then blanch them
Prepare the mushroom filling by melting 4 Tbsp butter in a pan
Add sliced mushrooms to the butter and cook until tender
Season mushrooms with 1 tsp salt and ¼ tsp pepper
Add 2 Tbsp garlic to the mushrooms
Sprinkle 4 Tbsp flour over the mushrooms and stir to combine
Pour in 12 oz chicken stock and 12 oz heavy cream
Stir in 1 Tbsp fresh chopped tarragon
Combine blanched green beans with the mushroom filling
Adjust seasoning for salt before adding green beans
Prepare the topping by toasting 4 slices sourdough bread and breaking into pieces
Mix bread pieces with 1 cup fried shallots, 1 tsp salt, ¼ tsp black pepper, and ¼ cup grated Reggiano
Drizzle 6 Tbsp melted butter over the topping mixture
Transfer green bean and mushroom mixture to a baking dish
Top with the bread and shallot mixture
Bake at 350°F for approximately 25 minutes until the top is golden brown
