Bring a large pot of salted water to a boil and cook the cubed potatoes until easily pierced with a fork, about 15-20 minutes, drain and return to the pot.
Using a potato masher or fork, mash the potatoes until no lumps remain.
Melt the butter in a small saucepan, remove from heat, and mix in the milk, heavy cream, dried minced onion, garlic powder, salt, and pepper.
Mix the creamy mixture into the mashed potatoes and stir until the potatoes are creamy and smooth. Add more milk if needed.
Taste the mashed potatoes and add more salt if needed. Serve with an extra pat of butter and freshly chopped parsley on top.