Preheat the oven to 375 degrees F. Rinse your potatoes and peel them. Cut each in half, then cut each of those pieces in half. If some of the potatoes are large, you may need to cut those pieces in half again.
Spread the potatoes in a single layer in a large glass pan. (I used a 10x15). If you don't have a pan that large, fit what you can in a 9x13 and put the extras in an 8x8. (Glass works better than a baking sheet.)
Sprinkle on the onion powder and Seasonello evenly. Slice the butter into squares ½-inch thick and scatter them on top of the potatoes.
Bake uncovered for 1 hour and 15 minutes, stirring once at the halfway point. The potatoes should be browned on some sides, but not all. For best texture, let the potatoes rest for 10 minutes before serving. Garnish with parsley, if desired.