Place potatoes in a large pot and add enough cold water to cover potatoes. Add 1 Tbsp salt and bring water to a boil.
Lower heat to a simmer and cook until potatoes are tender when pierced with a fork, about 15-20 minutes.
When potatoes are almost done boiling, melt butter in a small saucepan over medium heat. Add garlic and cook for 1-2 minutes, until aromatic and just starting to brown.
Turn heat to low and add milk and cream to the saucepan. Heat until hot, but not boiling.
Drain potatoes well using a strainer and return to pot. Mash with a potato masher until desired consistency is reached. Take care not to over-mash (I like to leave some chunks, but you can also mash until completely smooth).
Add hot garlic/milk/cream mixture, garlic powder, ½ tsp salt, and ½ tsp pepper to potatoes and stir to combine. Fold in parmesan cheese.
Serve mashed potatoes topped with chopped chives or scallions and more butter, if desired.