Preheat oven to 325°F.

Parboil Potatoes - Put the cubed potatoes in a saucepan and fill it with just enough water to cover the potatoes and 1 tsp salt. Bring to a boil, and simmer with the lid off until potatoes are tender, about 8 minutes if 1” cubed or 6 minutes for ½” cubed. There should be a little resistance with a fork when pierced. Drain, set aside to cool or cool in cold water.

In a medium saucepan, melt ¼ cup butter over low heat. Add the flour, salt and pepper, 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, red pepper, and green onions. Reserve a few for the top of the casserole if you'd like.

Pour the cheese sauce over the top of the potatoes.

In a small bowl, combine the bread crumbs and the 3 Tbsp melted butter. Mix well. Sprinkle the bread crumbs overtop the cheese-covered potatoes.

Bake at 325 degrees for 35-40 minutes, or until the casserole is bubbly and heated through.

Remove from oven. If you reserved a few of the green peppers and pimentos, add them to the very top of the casserole. Serve hot.