Fit a large pot with a steamer basket. Fill bottom with water. Add cauliflower to steamer basket. Cover. Bring to a boil and allow to steam 20 minutes.
Drain water. Return cauliflower to pot. Puree with an immersion blender. (Or puree in a traditional blender before returning to pot, taking care to vent the lid.)
Add butter, cheese, salt, and pepper. Stir until butter and cheese melt.
Instant Pot®
Add 1 cup water to instant pot. Add cauliflower. Seal, program for manual, high, and decrease time to 8 minutes.
When cook time ends, select either natural pressure release or quick release. Using an immersion blender, puree cauliflower. (The water can be drained for a thicker puree or included for a thinner puree.)
Add butter, cheese, salt, and pepper. Stir until butter and cheese melt.