Place ham, cut side down in baking pan with 3/4 cup of water and cover with foil
Bake ham 12-15 minute per pound
While ham is cooking you can prepare the glaze
Using a large skillet, melt the butter over medium heat
Add onions and cook until tender, stirring occasionally - about 3-5 min.
Add the tomato sauce, sugar, and Worcestershire Sauce
Bring the sauce to a boil, and cook for a few minutes until the glaze thickens up a bit
Remove from heat
When your ham is about 30 minutes away from done pull the foil off of the ham, and start brushing the ham with the glaze over 2 or 3 times each brushing
Continue to brush the glaze over the ham about every 10 minutes
Ham should have an internal temperature of 140 degrees F