Rinse, peel and cut the potatoes into 1" chunks.
Put the potatoes in a saucepan and fill the saucepan with enough water to cover the potatoes.
Boil the potatoes and the water on the stove. Let the potatoes simmer for about 10 minutes.
Add the cauliflower florets and garlic clove, and boil for another 10 minutes.
Drain the potatoes, cauliflower and garlic with a sieve or colander. Return the vegetables to the saucepan.
Use a potato masher to smash up the vegetables. Add in 1 tablespoon of butter and keep smashing as the butter melts.
Add the milk and the salt, and continue mashing until the potatoes and cauliflower are creamy and smooth.