Place potatoes in a medium pot and cover with water. Bring sweet potatoes to a boil over medium-high heat, then reduce heat and simmer until potatoes are fork tender. Drain potatoes and place on a greased baking sheet.

Roast sweet potatoes at 400F 20-25 minutes until potatoes are very tender. Remove from oven and immediately smash potatoes flat with a potato masher. Set aside for a moment.

In a small saucepan over medium-high heat, brown butter until a deep golden brown. Reduce heat to low and whisk in garlic and rosemary until fragrant.

Remove butter from heat and drizzle over smashed potatoes. Sprinkle Parmesan cheese over top and season with salt and pepper to taste.

Roast potatoes an additional 10 minutes at 400F until potatoes are crispy and cheese is melted. Enjoy warm!