Preheat the oven to 425°F. Place potatoes with rosemary sprigs, smashed garlic, ¼ cup of salt, and water in a saucepan.
Bring the potatoes to a boil over high and reduce to medium heat. Simmer until potatoes are tender when pierced with a fork. Drain the potatoes and discard rosemary sprigs and smashed garlic.
Line a baking tray with parchment paper. Brush the parchment paper with two tablespoons of oil.
Arrange potatoes on the prepared baking tray. Using the heel of your hand or the backside of a glass, lightly smash the potatoes until they are about ½ inch thick.
Brush with 1 tablespoon of oil. Bake in a preheated oven for 25 minutes until golden brown and crisp.
In a bowl, stir together butter, chopped parsley, thyme, rosemary, minced garlic, pepper, and the remaining 1 tablespoon oil and ½ teaspoon salt. Brush mixture over potatoes, and serve immediately.