Prep: Preheat that oven to 400F Cut potatoes into 1/4 inch slices to layer and boil them in salted water until soft While you wait for those, add your trimmed leeks to boiling salted water. They only need about 3-5 minutes Whisk the milk and egg together Layer: In a 13x9 casserole dish start to layer! Row of half your potatoes... sliced half of brie cheese wedge... half your cooked leeks The rest of your potatos and then tuck the leeks under and over the remaining brie Finally, pour your milk/egg mix over and top with foil. Cook 45 minutes foil on and then remove untill brown and melty! *You can easily add pre cooked ham to the layers for a quick 1 pan meal.