Fill a large pot with water and add a generous pinch of salt. Bring it to a boil over medium-high heat. Once boiling, add the peeled and chopped potatoes.

Let them cook for about 15–18 minutes. You’ll know they’re ready when a fork slides in easily without resistance. I usually test a few pieces because sometimes the smaller chunks cook faster.

Drain the potatoes well in a colander and let them sit for a minute or two so the extra steam escapes. This helps avoid watery mashed potatoes later.

Add the drained potatoes into a large mixing bowl. Start mashing them while they’re still warm. I usually don’t aim for complete smoothness here—some small lumps actually make the final dish better.

Add the butter first so it melts into the hot potatoes. Then mix in sour cream, milk, garlic powder, salt, and pepper.

At this point, it should start looking creamy but still thick. If it feels too stiff, add a splash more milk, but go slow. I’ve made the mistake of adding too much milk at once and ended up with soup-like potatoes. Not great.

Stir in 1 cup of the cheddar cheese and all of the Parmesan cheese. Save the remaining cheddar for the top.

This is where it starts smelling really good. The warmth of the potatoes melts everything together, and it gets that rich, almost velvety texture.

Grease a 9x13 baking dish lightly with butter or cooking spray. Spread the potato mixture evenly into the dish.

Sprinkle the remaining 1/2 cup cheddar cheese on top.

Bake at 350°F for about 20–25 minutes, or until the top is melted and lightly golden.

If you want a slightly crispier top, you can broil it for 1–2 minutes at the end. Just don’t walk away—I learned that the hard way when I nearly burned the top once.

Let it sit for about 5 minutes before serving. Sprinkle chopped green onions on top if you’re using them.