Hasselback potatoes are potatoes that have been sliced incrementally across without cutting all the way through. They're cooked and often stuffed with various ingredients.
Spread melted butter over the tops of the potatoes and sprinkle them with salt and pepper. Add the garlic to the leftover butter so you can add it after the potatoes are done.
When the potatoes are done baking, add the garlic butter to the tops generously. Return to the oven for about 10 minutes to crisp up with the additional garlic.