Preheat the oven to 350 degrees F (175 degrees C).
Cut potatoes in half lengthwise and scoop out the middle of each, leaving enough to keep the skin intact and stable.
Put the raw potato flesh into a food processor along with onion, 1/4 cup of Cheddar cheese, sour cream, garlic, salt, and pepper. Blend ingredients together until it is the consistency of a very rough puree (be sure not to blend to a paste). Spoon mixture back into potato shells; top with the remaining Cheddar and sprinkle with bread crumbs.
Bake in the preheated oven until tender, about 1 hour.