In pot used for potatoes, heat 1 TBSP butter, remaining chopped rosemary, and remaining garlic over low heat. Once garlic is fragrant, about 30 seconds later, remove pot from heat and add potatoes and ⅓ cup milk (you’ll have some left over). Mash with a potato masher or fork until smooth. Season generously with salt and pepper. TIP: Add more milk, if needed, to give potatoes a creamy consistency.