Ingredients
1 tablespoon unsalted butter
2 small heads fennel, finely chopped (about 3 cups)
1/2 medium yellow onion, finely chopped
2 medium carrots, peeled and finely chopped (about 2/3 cup)
12 ounces white button mushrooms, sliced (about 5 cups)
1 small russet potato, peeled and diced small (about 2 1/2 cups)
1/4 cup all-purpose flour
1 cup low-sodium mushroom broth
1 cup whole milk
1 cup frozen baby green peas
1/4 cup thinly sliced fresh chives
1/4 cup parsley
1 tablespoon white vinegar
1 large egg yolk
7 ounces store-bought puff pastry or pie dough, defrosted if frozen