Start by peeling the potatoes. Give them a good wash, and cut the potatoes into halves if they're small or quarters if they are large. Try your best to keep them uniform so they cook evenly.

Place the potatoes in a large pot, and cover with at least 2 inches of water. Place the pot over medium-high heat and bring to a rolling boil. Cook for 18-20 minutes, just until they are fork tender. Don't overcook the potatoes or they will absorb too much water.

Drain the potatoes well. Do not rinse!

Mash the potatoes with a masher, press them through a ricer, or mash them with a hand mixer or stand mixer until smooth. Immediately stir in the garlic to let the risidual heat "cook" the garlic a bit.

Stir in the white cheddar cheese until melted. Add the butter, sour cream, rosemary, 1/2 teaspoon of Kosher salt, and a few dashes of white pepper. Then, add 1/3 cup of the half-and-half. Add more half-and-half, one splash at a time, until you reach your desired consistency.

Taste and add more Kosher salt and pepper, if necessary.

If you're making these in advance, spoon the mashed potatoes into an airtight container and let them cool to room temperature, stirring occasionally to help speed up the process. Store covered in the fridge for up to 3 days.

BAKE: This is the method I recommend! To reheat the mashed potatoes, preheat the oven to 350°F. Spoon the potatoes into a lightly greased dish and stir in a splash or two of half-and-half to loosen them up a bit. Bake for 20-30 minutes until hot and bubbly.

MICROWAVE: Alternatively, place the potatoes in a microwave-safe bowl. Cover and microwave on high for 1 minute. Stir, and continue cooking 1 minute at a time until hot. Add half-and-half or butter as needed.