Place potatoes and peeled garlic in a large saucepan; cover with water and then bring to a boil over high heat.
Reduce the heat to low and cover the saucepan.
Simmer the potatoes for about 20 minutes, or until fork tender.
Remove from heat and drain the potatoes and garlic thoroughly and return to the saucepan or to a large mixing bowl.
Meanwhile, using a cup. combine the milk and butter and microwave until hot.
Add the hot milk and butter mixture to the potatoes; mash until smooth, adding salt and pepper, to taste.
Stir in the Parmesan cheese, if using.
If using an electric mixer, avoid overmixing.
Notes
For perfectly smooth mashed potatoes, put the cooked potatoes and garlic through a potato ricer. The riced potatoes will mash beautifully with no lumps to worry about.