Preheat oven to 375 degrees. Butter a 9 by 13 inch (or similar) baking dish with 1 tablespoon butter.
Melt the remaining 3 tablespoons butter in a large skillet over medium heat. Add the leeks and sauté until tender, about 5 minutes. Put the leeks in the prepared baking dish.
Combine the Gruyere and Parmesan cheeses. Put all but ½ cup of the mixture on top of the leeks. Whisk together the eggs, cream, chives, salt, and pepper. Pour into baking dish.
Cut the cream cheese into small pieces and dot over the eggs. Sprinkle the remaining ½ cup mixed cheese over the top of the eggs and bake for 30 – 40 minutes or until the eggs are set and the edges are starting to brown. Garnish with fresh chives if desired and serve.