Place the potato chunks in a large saucepan and cover them with cold water by about 1 inch. Add approximately 1 teaspoon of the kosher salt.

Bring the water to a boil, then reduce the heat and simmer for 15 to 20 minutes. Cook until the potatoes are fork-tender but still hold their shape rather than falling apart.

Drain the potatoes thoroughly, return them to the warm saucepan, and let them sit over low heat for 1 to 2 minutes. This evaporates excess moisture before the dairy is added.

Warm the butter and milk or half-and-half together in a small saucepan or microwave-safe container. Heat until warm and the butter melts, but do not let the mixture boil.

Mash the potatoes by hand with a potato masher, gradually adding the warm butter mixture. Stop when the potatoes are creamy but still contain a few small chunks.

Stir in the remaining salt, freshly ground black pepper, and optional sour cream or cream cheese. Taste and adjust the seasoning as needed.

Serve the mashed potatoes immediately with additional butter and chopped chives or parsley if desired. Keep the texture rustic by stirring gently rather than beating the potatoes.