3 potato gruyere oyster gratin Recipes

unsalted butter, plus more for baking dish, onion, finely diced, mushrooms (such as shiitake, chanterelle, oyster), washed, dried, and coarsely chopped, white wine, salt (to taste), freshly ground black pepper, grated gruyere cheese, grated parmesan cheese, yukon gold potatoes, peeled, fresh thyme, heavy cream

butter, oyster mushroom, halved if large, garlic, minced, leeks (white and pale green parts only, about 4 large, thinly sliced), fresh thyme, minced, chicken broth, whipping cream, dry white wine, salt, black pepper, russet potatoes, peeled, thinly sliced into rounds (about 8 cups), gruyere cheese, grated (about 10 oz)