Prepare a large bowl with an ice bath and set aside.
In a small pan over medium heat, add butter and melt. Once melted, toss in the rosemary and garlic.
Whisk butter continuously until the butter has browned. Keep an eye on it as this can happen quick!
Once the butter is brown, immediately transfer to a small bowl. Remove the rosemary and garlic. (you can fish out all the rosemary leaves, as I did, or you can just remove the sprig if you want some whole rosemary left in the butter)
Place small bowl with butter mixture over the large ice bath. Whisk butter mixture, constantly, until the butter becomes light in color and has a whipped consistency.
Fold in pecorino. Season to taste with salt and pepper.
Enjoy!
Notes
* Make sure rosemary sprig is completely dry! Any water on it can make the butter pop while browning and it can get messy/hazardous