Mushroom and Leek Tart with Gruyere Cheese

4 Servings12 ingredients
1 sheet frozen puff pastry thawed
1 tablespoon unsalted butter
1 tablespoon olive oil
2 whole leek white and light green parts only, thinly sliced
8 ounce cremini mushroom sliced
2 whole garlic clove minced
1 teaspoon fresh thyme chopped
0.5 teaspoon salt
0.25 teaspoon black pepper
0.5 cup heavy cream
2 whole large egg
1 cup gruyere cheese grated