Preheat oven to 350 degrees F.
To prepare broccoli rice, wash and thoroughly dry broccoli. Cut florets from stalks. Peel outer layer of flesh off of stalks and cut into small pieces. Add everything to a food processor and pulse several times until broccoli is finely chopped.
Measure out 2 cups of broccoli rice. Use any excess broccoli rice for another purpose.
Mix 2 cups of broccoli rice, onion, cheddar cheese (and salt and pepper if using) in a large bowl.
Stir egg into broccoli mixture.
Scoop mixture into mini or regular muffin tins coated to prevent sticking. The yield will be about 24 mini muffins or 8-9 regular sized muffins. Note: the mixture settles as it cooks so overfilling the muffin tin is ok. However, you may end up with less than the quantity specified.
Press mixture down with the back of a spoon or fingers.
Bake for 20 minutes or until firm and starting to brown.
Gently remove from tins and enjoy!