Butter an 8-by-10-inch baking dish and line it with the tortillas. In a large bowl, whisk the eggs with the egg yolks. Add the cream and milk and whisk to blend. Stir in the leeks, corn, 2 teaspoons salt and 1/4 teaspoon pepper. Pour the custard over the tortillas. Cover and refrigerate overnight. Bring to room temperature before baking.