Heat oven to 325 degrees. Remove packaging (and circle over bone if included) and trim fat from ham if needed. (You can score the ham if you want now - I usually don't bother.)
Place ham in a shallow roasting pan, cut side down. Add 1/2 cup water to pan for hams 4-6 pounds and 1 cup of water for 7-8 pounds or larger. Cover with foil (TIP: place a piece of parchment on top of ham before foil so that foil wont' touch the top of the ham).
Bake about 15-18 minutes per pound.** Examples: a 4-pound ham would need 1 to 1.5 hours and an 8 pound ham would need 2 to 2.5 hours. Regardless of size, the final temperature should be 140 degrees for a fully cooked ham (or 160 degrees for a "cook before eating" ham).
GLAZE: 30 minutes before ham is scheduled to be done, remove from oven and turn oven up to 400 degrees. Remove foil (save to tent the ham later) and brush with HALF the glaze. Return to oven for 15 minutes, uncovered. Remove from oven and brush the remaining glaze over the ham and cook 15 minutes more or until a thermometer reads 140 degrees (or 160 degrees if your ham wasn't sold fully cooked).
Remove the ham from the oven and let rest, covered with the foil, 20-30 minutes before carving.
Make Ham Sauce
Microwave: Put eggs, cornstarch, sugar, salt, and mustard in a 4 cup or larger glass bowl and whisk until no lumps remain. Then whisk in milk and vinegar.
Cook on HIGH for 3 minutes. Stir well. Cook on ROAST for 4 minutes longer or until thickened.
Stovetop: Add eggs, cornstarch, sugar, salt, and mustard to a medium saucepan and whisk until no lumps remain, then add milk and vinegar, whisking until smooth.
Bring to a simmer over medium-high heat, about 2-3 minutes, stirring occasionally. Lower heat and stir until thick, only about 30 seconds more. Remove from heat.
Store ham sauce in the refrigerator. Serve chilled with ham or heat slightly to avoid chilling the ham.
Notes
Glaze Options:
Maple-Mustard: 1/4 cup maple syrup + 2 Tablespoons Dijon mustard for 4-5 pound ham; 1/3 cup syrup + 1/4 cup Dijon mustard for 6-8 pound ham.
Orange-Honey: 1/3 cup honey + 1/4 cup orange juice
*For most meals where there are multiple side dishes you can plan on 1/2-pound of ham per person. If ham is more the star, 3/4-pound per person.**Minutes per pound is a guideline for timing - the MOST important thing is to make sure the ham is at the safe temperature before you remove it from the oven, which is 140 degrees, minimum for a fully cooked ham (160 degrees for a cook-before-eating-ham).Storage: You can keep slices of ham in an airtight container in the fridge for 4-5 days. TIP: Spoon pan juices over slices to help keep moisture in while refrigerated.Reheating: To avoid drying out a number of slices, heat them in a low oven in a covered container for 10-15 minutes or until warmed through or microwave slices for about a minute.Freezing: Ham freezes beautifully! Portion the slices however you want into airtight freezer containers or baggies and freeze for 3-4 months for best quality.Nutrition calculated for a 1/2 pound serving of a 5-pound ham with maple-mustard glaze and a couple tablespoons of mustard sauce (an approximation).