Preheat oven to 375 degrees Fahrenheit.

In a skillet, heat oil. Fry mushrooms over low heat for 10 minutes, stirring occasionally.

In a medium mixing bowl, whisk eggs, milk, heavy cream, salt, and pepper. Set aside.

Divide mushrooms evenly among the tart shells. Sprinkle shredded cheese over them. Pour the egg mixture over the cheese and stir gently.

Place on the bottom rack of the oven and bake uncovered for 20–25 minutes.

Allow to set for 20 minutes before serving.