Step 1

Set the oven rack to the center position. Preheat your oven to 400 degrees F (200 degrees C).

Step 2

Place the garlic in a center of a piece of foil that's large enough to completely wrap the garlic. Optionally, cut the top of the garlic cloves so they are exposed.

Step 3

Generously drizzle olive oil over the cut garlic cloves then tightly wrap the head of garlic in the foil and place on a baking sheet.

Step 4

Roast the garlic in your preheated oven for 40 to 60 minutes. The garlic cloves will be soft enough to easily pierce with a fork, golden brown and extremely fragrant. Let cool enough to touch.

Step 5

Squeeze the garlic cloves from their paper skin into a small bowl or container. Set aside.

Step 6

Peel the russet potatoes and cut them into smaller, equal-sized pieces.

Step 7

In a large pot, add the potatoes and add enough water to cover them over an inch above the top of the potatoes. Add the tablespoon of kosher salt and bring the pot of water to a boil.

Step 8

Boil until the potatoes are fork-tender, about 20-30 minutes. Drain the potatoes in a colander.

Step 9

Mash the potatoes or push them through a potato ricer back into the pot or into a large serving bowl.

Step 10

Melt the unsalted butter in a microwave-safe container with the sprig of rosemary until fully melted.

Step 11

Remove the rosemary sprig from the butter then stir the unsalted butter into the potatoes. Gently fold and mix in the roasted garlic and milk with a wooden spoon until well combined and the butter and milk are absorbed. Smash the garlic against the sides of the bowl as well to help incorporate great flavor.

Step 12

Taste the mashed potatoes and season with salt and pepper as needed.

Step 13

If needed, rewarm the potatoes in the same pot over medium-low heat, stirring occasionally.

Step 14

Serve warm to hot.

Step 15

Keep in an airtight container in the fridge for up to 4 days.