Use chopsticks or two identical wooden spoons to hold potatoes steady for cutting and to make sure you do not cut through to the bottom of the potato. Position potato the long way between them, begin at the end and start cutting down the potato in ¼” slices until you reach the end.
Add a ¼ inch piece of butter between every other slice in each potato. Sprinkle the potatoes with garlic powder, salt and pepper. Then drizzle with olive oil and bake at 375° for 40 minutes.
Remove from oven and sprinkle potatoes with cheddar cheese and put them back in the oven for 10 more minutes.
Remove and sprinkle scallions over potatoes. Add sour cream if desired.