Preheat the oven to 400 degrees
Line a large rimmed baking sheet with parchment paper. Smash the garlic cloves and set aside.
Pour the avocado oil on the baking sheet and lay the garlic cloves and rosemary on the sheet pan as well.
Hold the end of one potato. Use a sharp knife to cut across the potato to create 1/8-inch sections. Do not cut through the potato but cut two-thirds the way down, leaving at least a 1/2 inch solid base at the bottom. Repeat with the remaining potatoes.
You can use 2 wooden skewers on each side of the potato as a guide.
Place the potatoes on the baking sheet and roll them around to cover them with the oil. Set them cut-side-up and top each potato generously with salt and pepper.
Roast in the oven for 30 minutes. Use a pastry brush to brush the herb-infused pan oils over the top of each potato and in between the folds.
Roast in the oven for another 30 minutes, until the potatoes are fork tender.
Top with some parmesan cheese the last 5 min of baking, if desired.