Preheat oven to 350 degrees. In a 12x8 inch greased bakingdish, line the bottom with tortillas. In a bowl, add the beaten eggs and buttermilk and beat again. Add cheese, ham (or sausage), and onion and mix thoroughly.
Pour mixture over tortillas. Bake 35-40 minutes, until firm. Cut into serving squares. Garnish with jalapeno peppers. This casserole is delicious and easy - serve with plenty of picante sauce, refried beans with cheese and hot flour tortillas.