Peel the potatoes and cut them into uniform 1-inch cubes. Rinse the potato cubes thoroughly under cold water to remove excess starch. Place the rinsed potatoes in a large pot and cover with cold water by about an inch. Add 1 teaspoon of kosher salt to the water.

Bring the water to a boil over high heat, then reduce heat to medium-low and simmer until the potatoes are fork-tender, about 15-20 minutes. Be careful not to overcook them into mush.

Once tender, drain the potatoes completely in a colander. For the creamiest results, return the drained potatoes to the empty hot pot and cook over low heat for 1-2 minutes, shaking the pot gently, to evaporate any remaining moisture. This step is crucial for non-watery mashed potatoes.

While the potatoes are drying, in a small saucepan, gently heat the milk (or half-and-half) and butter over low heat until the butter is melted and the mixture is warm, but not boiling. Stir in the minced garlic. Remove from heat.

Transfer the hot, dry potatoes to a large mixing bowl. Using a potato masher or ricer, mash the potatoes until mostly smooth with a few small lumps, or to your desired consistency. Avoid over-mashing, as this can lead to gluey potatoes.

Gradually pour the warm milk, butter, and garlic mixture into the mashed potatoes, stirring gently with a spatula or wooden spoon until just combined and creamy. Stir in the fresh chives, parsley, and rosemary (if using).

Taste the mashed potatoes and add the remaining 1/2 teaspoon of kosher salt and freshly ground black pepper. Adjust seasonings as needed. Serve immediately.