2 cups mashed potatoes
1 cup cheddar cheese, shredded
1/2 cup Monterey Jack cheese, shredded
1 cup Gouda Cheese, shredded
2 cups all purpose flour
2 tablespoons carnations milk powder
2 cups crackers crumbs
Salt and pepper to taste
Oil for frying
Mix the mashed potatoes, flour, egg yolks, milkpowder, salt and pepper in a large bowl
Set aside. In 2 separate bowls place crackers crumbs and white eggs. 
Mix the cheese in a bowl. 
Place about 1/4 cup of potato mixture in the palm of your hand. Flatten it slightly and place with cheese mixture. Fold the potatoes over the cheese to close it completely and shape the potatoes into an oblong croquettes. Repeat with the remaining potatoes and coat with egg whites and crackers crumbs. Place on a plate or baking sheet.
Heat 1/2 inch oil in a 12 inch heavy skillet over medium high heat until it shimmers. Fry croquettes in batches, turning occasionally until golden brown. Transfer to paper towels to drain. .