First, blanch the broccoli. Fill a large pot a little over halfway with water and bring it to a boil on the stove. Salt it generously. Set up a bowl of ice water as well. Boil the broccoli head for just about a minute, then remove it right into the ice bath to stop the cooking. Cut the broccoli into manageable pieces, then transfer it to the bowl of a food processor. Also add the onion, garlic, dill and parsley. Pulse the mixture until it is a fine texture, then scoop it into a large mixing bowl. Add the egg, corn meal, cheddar, salt and Sriracha. Mix it all together thoroughly. Put the bowl in the fridge to chill the mixture for 15 minutes.