Instructions

1. Roll out your pie crust into a roughly 9-inch circle. Place on a sheet pan lined with parchment paper, and set aside.
2. Preheat the oven to 425 degrees F.
3. In a large skillet over medium heat, combine 3 tbsp of olive oil, garlic, leeks, salt, pepper, and thyme. Cook, stirring occasionally, until the leeks are soft, about 4 minutes.
4. Push the leeks to the perimeter of the pan, then add the remaining 1 tbsp olive oil and the mushrooms.
5. Cook until the mushrooms have given off their juices and then shriveled, about 10 minutes, leaving the leeks on the perimeter. Once mushrooms are cooked, fold the leeks in.
6. Sprinkle the gruyere over the rolled-out pie crust.
7. Spoon the mushroom-leek filling into the center, spreading it in an even layer and leaving a 1-inch border. Then fold the edges of the crust over the filling, overlapping as you work your way around the perimeter.
8. Brush the dough with the whisked egg and sprinkle with the sea salt.
9. Bake in the heated oven until the crust is golden, 20 to 25 minutes,