Place cauliflower in a steamer over a large pot of boiling water. Steam for 20 minutes until tender when pierced with a fork. Remove the steamer and cover with a lid or dish towel and set aside.

Dump out boiling water from the pot and place the pot back on your stovetop. In the same pot, heat the butter over medium high heat. Sauté garlic until fragrant (about 1 minute) then let simmer on low.

Blend cauliflower and garlic butter in a food processor on high setting until smooth. You may need to do this in batches of two or three, depending on the size of your processor.

Transfer blended cauliflower into the pot. Stir in the Parmesan cheese, sour cream and season with salt and pepper.