Preheat Oven to 350° OR you can bake this in a casserole slow cooker.
Spray 9 x 13 glass baking dish, or casserole slow cooker, with non-stick cooking spray.
Place cubed washed potatoes in the bottom of your baking dish.
Top with thawed, frozen vegetables.
In a medium skillet, over medium heat, saute sliced beef smoked sausage, onions, and sweet peppers until onions and peppers are tender and sausage is slightly brown.
Place Sausage mixture on top of Vegetables in baking dish.
In the same medium skillet, over medium heat, melt 4 Tablespoons of butter. Whisk in 3 Tablespoons of flour until thick paste forms.
Add 2 cups of milk. Whisking constantly until mixture thickens.
Add 1 4oz. pouch of Velveeta Cheese and 1 1/2 cups of grated cheese. Stir until smooth and cheese has melted to create a rich cheese sauce Salt and Pepper to taste.
Pour Cheese sauce over ingredients in baking dish. Top with remaining 1/2 cup grated cheese.
Cover with foil if baking in oven. Place Slow cooker lid on top of dish if baking in your slow cooker.
Cook in Oven for 1 hour and 15 minutes at 350° stir, gently, half way through baking. Remove foil for last 10 minutes of cooking.
Cook on LOW for 4 hours if using your casserole slow cooker, or until potatoes are tender. Stir, gently, half way through baking.
Garnish with fresh parsley.
Serve.