In a heatproof bowl, mix the cauliflower, cream cheese, half-and-half, Cheddar cheese, salt, and pepper together. Cover the bowl with aluminum foil. Pour 2 cups of water into the inner cooking pot of the Instant Pot®, then place a trivet in the pot. Place the bowl on the trivet. Lock the lid into place. Select Manual or Pressure Cook and adjust the pressure to High. Cook for 5 minutes. When the cooking is complete, let the pressure release naturally for 10 minutes, then quick-release any remaining pressure. Unlock the lid and carefully remove the bowl. Remove the foil. Place the cooked cauliflower under the broiler, and broil until the cheese is brown and bubbling, 3 to 5 minutes. Serve immediately.