Preheat oven to 400 degrees F.
Boil potatoes approximately 15 minutes or until tender such that they can be pierced easily with a fork but not fall apart.
While potatoes boil, combine, rosemary, salt and pepper in a small bowl.
Drain potatoes and place in a large bowl or directly on the baking sheet.
Toss the cooked potatoes with 1-2 tablespoons olive oil and some of the rosemary salt.
Transfer to baking sheet if not already on it.
Using the bottom of a jelly jar or measuring cup, press the potatoes down until they "smash" a bit, so that you can see both the skin and the center of the potato. They will hold together mostly (don't worry if a few don't! They were probably cooked a bit more than the others which will happen unless your potatoes are exactly the same size). Keep potatoes separate and not touching as you continue to smash them so that they crisp when they cook.
Sprinkle with additional rosemary salt to taste.
Bake for 20 minutes.
While the potatoes bake, smash the garlic with a jar or knife, or if you're more comfortable, slice it in half.
After 20 minutes, remove potatoes from oven and flip them so that both sides crisp up nicely. Add garlic to the baking sheet with the potatoes. Top each potato with a dab of butter or olive oil, or just place some butter or olive oil on the pan along with the garlic.
Return to oven and bake an additional 20 minutes.
Serve and enjoy!