Beat the eggs in a bowl until smooth. Stir in the salt, pepper, cheese, milk, and cream. Mix the leeks.
Reduce the oven temperature to 375 degrees. Pour the filling into the precooked shell while the pan is still on the cookie sheet in the oven. (The filling will come to the rim of the shell, and there is less likelihood of it spilling if the pan is not removed from the oven.) Bake for 20 to 25 minutes, until the filling is completely set beautifully browned on top.
Let the quiche rest for 10-15 minutes before cutting it into wedges and serving.