Roll out the pie dough to about 1/8-inch thick and place it into a 9-inch pie plate. Trim and flute the edges, then chill in the refrigerator.

Melt 1 tablespoon of butter in a skillet over medium heat. Add chopped leeks and sauté for 2-3 minutes until tender. Remove from heat.

In the same skillet, melt 2 tablespoons of butter. Add sliced mushrooms and cook for 4-6 minutes until tender. Mix in leeks, salt, and pepper, then let cool.

Preheat oven to 375°F (190°C). Sprinkle half of the cheddar cheese in the chilled crust, add the cool mushroom and leek mixture, and top with remaining cheese.

Whisk together eggs and heavy cream in a bowl, then pour over the filling in the pie.

Bake the pie for 30-35 minutes until the center is set and a knife comes out clean. The crust should be golden and the top puffed.

Let the pie cool for about 10 minutes before slicing. Garnish with fresh parsley if desired.