Peel and cube the potatoes and boil them in water to cover with 1 t. salt. Cook until a fork goes through a cube, drain and set aside.
Sauté the vegetables in the butter over medium low heat with a pinch of salt. Cook slowly until the vegetables are beginning to brown. Add the flour and stir constantly for a minute or two. Add the buttermilk and stir until the sauce coats a spoon.
While the vegetables are cooking, grate ½ the block of cheese. Cut the other half in ½” cubes.
When the sauce has thickened, take it off the heat and stir in the grated cheese. Stir until the cheese is melted. Season to taste with salt, pepper, and the garlic powder. The sauce should be highly seasoned because potatoes are bland.
Fold together the drained potatoes, cheese sauce, cubed cheese, bacon, and parsley. Put into a casserole dish and sprinkle with the breadcrumbs. Bake at 350° until potatoes are bubbly and the breadcrumbs are browned.