Ham drippings can vary greatly so great gravy relies on tasting and adjusting, not exact measurements.
Remove ham from roaster to serving platter and cover. Place roasting pan over a medium flame and use a wooden spoon to release concentrated flavor from the pan, stir and simmer to dissolve. Strain any excess fats. Can be strained into a saucepan at this point, or continue in roasting pan.
Taste drippings, if they’re too strong, add water, milk or both – if they are too watery, simmer to reduce - the goal is pan juices with a rich gravy-like taste that are ready to thicken. If the drippings are still too sweet or salty, making gravy is not recommended.
Estimate total pan juice volume in cups and allow about 2 TBS of Wondra flour per cup, or 1.5 TBS of All Purpose Flour per cup.
Sprinkle Wondra flour into simmering juices a little at a time while whisking vigorously. Continue to whisk until smooth and free of lumps and then simmer until thick and rich, stirring regularly.
For richer gravy: Blend Wondra or AP flour into an equal amount of unsalted butter with a fork or your fingers. Add 1 tsp sized lumps to simmering pan juices while stirring with a whisk to dissolve, repeat and continue to whisk until the sauce is smooth and free of lumps. Continue to simmer until thick and rich, about 5-10 minutes.