Wrap ham entirely in tin foil or place in an oven-safe roasting bag -- this keeps it moist!
Bake ham for 2.5-3 hours, or roughly 40 minutes per kg. Remember that the ham is fully cooked (be sure to check your label), so you are simply heating through. You don't want to overcook and dry out your ham!
Remove the ham from the oven and let rest for 15 minutes before serving. While the ham is resting, make the glaze.
In a medium saucepan, whisk together the cider, sugar and corn starch.
Bring to a boil over medium-high heat, then reduce heat to simmer until thickened. Taste and adjust seasoning as desired.