Coal Cracker Casserole - Jake & Amos

Ingredients

• 1 - 16 oz. jar Jake & Amos Sauerkraut
• 1 teaspoon canola oil
• 1 pound Polish Kielbasa sausage, 1-inch slices
• 1 Tablespoon butter
• 1/2 onion, sliced
• salt
• freshly ground pepper
• 1 Tablespoon stone-ground mustard
• 1 cup chicken stock or beer
• 1 pound frozen potato and cheese filler pierogies, precooked and drained
• 1 cup cheddar cheese, grated
• 1 cup swiss cheese, grated
• scallions, chopped