In a large bowl, combine the cream cheese, sour cream, egg and lemon juice with an electric hand mixer until smooth.
Stir in the cheddar, garlic, onion, nutmeg, salt and pepper.
Fold the broccoli into the mixture and ladle into buttered casserole dish(es).
Cover the casserole(s) with foil.
Pour the water into the pressure cooker pot.
Place the casserole(s) onto the trivet in the pot.
If using mini casserole dishes, be sure to stack them firmly so they don't tip over during the pressure cook.
Place the lid on the unit and turn to locked position.
Turn the steam release valve to sealing.
Press the manual button and adjust the timer to 15 minutes.
Once the unit has finished cooking and the timer has counted to zero, allow the steam to release naturally for 10 minutes.
Carefully release any remaining steam.
Remove the casserole(s) and the foil from the tops.
Sprinkle cheddar on top for garnish and serve.