I absolutely love garlic mashed potatoes. I make garlic mashed potatoes and don't use specific measurements. I make them for two my husband and I so you will have to adjust according to how many need to be fed.
I take two large potatoes, wash, peel and cut into one and a half inch cubes. Put the potatoes in a pot and cover with water. Then take two cloves of garlic, peel and dice them and add them to the water as well. I throw in some salt and then boil for about 20 minutes, or until the potatoes slide off a fork when pierced.
Drain the potatoes and mash with a potato masher. I add about a half a stick of butter, more salt and some pepper and about half a cup of milk and stir until everything is blended. I don't bother heating the milk, because I mix it all up while still in the pan on the warm burner. Taste the potatoes, add more butter, pepper or salt as needed. Sometimes they aren't garlicky enough for me so I will sprinkle in some garlic powder.
When the potatoes are mixed, I sprinkle some dried parsley (you could also use freshly diced parsley) on top and dish onto plates with whatever meat and vegetables we are having.