Melt butter in small sauté pan over medium heat. Add chopped onions and cayenne pepper and sauté until onion turn brown. Set aside to cool.
Combine cream cheese, 1 cup cheddar cheese, Worcestershire sauce, and onion.
Chill briefly if necessary for handling, then form into a ball and roll in remaining cup of cheddar cheese. Pressing cheese on ball to fully cover the outside.
Place cheeseball on serving plate and using the rounded handle of a wooden spoon or similar object, make vertical groves in the ball to resemble a pumpkin. Push a 2 or 3 inch segment of broccoli stem into the top of the ball and place leaf beside it. Chill until ready to serve. Serve with crackers, cross sections of broccoli stems or other assorted vegetable slices.