Preheat oven to 350 degrees and spay a shallow baking dish with non-stick cooking spay. Melt the butter in the bowl and whisk in the paprika, salt, pepper and parsley flakes, mixing well. Toss the potatoes in the butter mixture until all are well coated. Add the onions (optional) and toss again. Transfer the potatoes to the baking dish and bake for 45-60 minutes uncovered, turning and checking for doneness about halfway through the cooking time. Continue cooking until potatoes are tender. The smaller you dice the potatoes the quicker they will cook.