Bring a large pot of water to a boil. Meanwhile, peel and cube the potato.
Once boiling, add potato and cauliflower to the pot of water. Allow water to return to a boil, and then reduce heat to medium. Simmer until very tender, 15 to 20 minutes.
Remove from heat and drain. Transfer contents to a large bowl. Add half-and-half, butter, 1/4 teaspoon salt, and crushed garlic, if using. Mash it all together with a potato masher, until completely blended.