Start by peeling the Russet potatoes and cutting them into equal-sized chunks, roughly 1–2 inches each. Place the potato chunks in a large bowl of cold water.

Transfer the potato chunks to a large pot, cover with cold water, and add a pinch of salt. Bring to a boil, then reduce to a simmer and cook until fork-tender, about 15 to 20 minutes. Drain the potatoes.

Return the drained potatoes to the pot over low heat to evaporate any leftover moisture for 2–3 minutes.

In a separate saucepan, warm the heavy cream, whole milk, and unsalted butter over low heat until the butter melts.

Mash the potatoes and gradually incorporate the warm dairy mixture until creamy. Avoid over-mixing to keep the texture fluffy.

Season with salt, pepper, and garlic if using, adjusting to taste.

Serve the mashed potatoes in a dish and top with a pat of butter to melt.