Preheat oven to 375 Degrees Fahrenheit

In a skillet over medium heat pour the olive oil

In a bowl, mix the eggs, mascarpone cheese and 1/2 cup of the Gruyere Cheese. Add salt and pepper

Toss the leeks into the skillet and cook until they soften, 3-4 minutes. Add the mushrooms and let them cook for 3-4 minutes. Pour in the egg mixture and let it cook in the skillet for 2 minutes or until the eggs begin to set on the sides. Sprinkle in the rest of the Gruyere cheese

Place the skillet in the oven and let the frittata cook for about 8 to 10 minutes or until the eggs brown and set.

Carefully remove the skillet from the oven using an oven glove or a kitchen towel and sprinkle the basil on top.