In a medium saucepan, melt the butter over low heat. Add the flour, salt and pepper, then use a whisk to blend it in. Gradually stir in the milk. Cook and whisk this mixture over medium-low heat until it is smooth and thickened, about 5 minutes. Remove from the heat.
Add the cheese to the sauce pan and mix until smooth.
In a lightly greased 1 1/2 quart casserole dish, add the cooked potatoes, green pepper and pimentos. Stir slightly. (Reserve a few of the peppers and pimentos for adding on top of the cheese sauce if you'd like. It gives a pop of color.)
Pour the cheese sauce over the top of the potatoes. Gently stir to distribute the cheese sauce evenly. Sprinkle any reserved pimentos & peppers on top.
In a small bowl, combine the bread crumbs and the melted butter. Mix well.
Sprinkle the bread crumbs overtop the cheese covered potatoes.
Bake at 325 degrees for 40-45 minutes, or until the casserole is bubbly and heated through.
Garnish with freshly snipped parsley.
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Notes
The calories shown are based on the recipe being divided 7 ways, with 1 serving being about 3/4 cup. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate.