4 tablespoons olive oil
1 1/2 pounds mushrooms (such as cremini or button), halved, or quartered if large
4 carrots, cut into 1/2-inch pieces
3 celery stalks, sliced 1/4 inch thick
1 medium onion, chopped
1/2 teaspoon dried thyme
kosher salt and black pepper
1/3 cup all-purpose flour
1 1/2 cups vegetable broth
1 cup frozen peas
1 sheet puff pastry (half a 17.3-ounce package), thawed