Preheat oven to 450°F. Make cuts on top of each potato, 1/8 inch apart, being careful not to go all the way through. Place wooden spoons along each side of the potato, which will help prevent cutting all the way through.

Place potatoes on a shallow baking sheet. In a small bowl, combine the olive oil and crushed garlic. Using a pastry brush, brush the tops of the potatoes very well, making sure some of the oil gets between the cuts. Sprinkle very generously with salt and pepper. Bake uncovered for 1 hour and 30 minutes. The potatoes will fan out while baking. Serve with balsamic mayonnaise dipping sauce.