Position one potato in between two wooden spoons. Cut vertical slits (⅛ inch apart) in the potatoes, cutting straight down until your knife hits the wooden spoon, leaving the bottom intact. Repeat this cutting process for the remaining potatoes.
Ina large mixing bowl, combine melted butter, olive oil, balsamic vinegar, maple syrup, rosemary, salt and black peppercorn. Add the potatoes and garlic cloves to the balsamic glaze; toss well. Make sure the potato slits are properly coated with the glaze.
Place potatoes and garlic cloves on a baking sheet. Oven roast for 60 minutes, or until potatoes are fork tender. Remove from oven and place potatoes into a medium deep-dish serving tray. Pour the rest of the balsamic glaze over the potatoes, if desired. Garnish with rosemary sprigs and serve immediately. Serve with olive oil infused with crushed red pepper.