Bring a large pot of salted water to a boil.
Add diced potatoes and cook until fork-tender, about 15–20 minutes.
Drain well and return to the pot to steam off excess moisture.
In a small saucepan, melt butter over medium heat.
Add minced garlic and sauté for 1–2 minutes until fragrant, being careful not to burn it.
Remove from heat.
Use a potato masher or hand mixer to mash the hot potatoes until smooth.
Gradually add the garlic butter and heavy cream, mixing until creamy and lump-free.
Fold in shredded cheddar and Parmesan until melted and fully incorporated.
Season generously with salt and freshly ground black pepper.
Spoon into a serving bowl, top with chopped chives or parsley, and serve warm.
