In a heavy skillet over medium heat, crumble the sausage with a fork. Saute the sausage until completely cooked. Drain off the fat, remove the sausage, and set aside. Melt the butter in another skillet over medium heat. Saute the onions in the butter until tender. Add the milk and heat until steam rises, but do not boil the milk. Cut the cream cheese into small pieces, add it to the onion mixture, and remove the pan from the heat. In a large bowl, beat the eggs, then add the cheddar, the onion mixture, the Worcestershire, salt, and pepper. Mix thoroughly and pour this into the piecrust. Top with cooked sausage, and bake for 30 minutes, or until set.