Mix reserved pineapple liquid, marmalade and mustard until well blended. Reserve 3/4 cup of the mustard mixture to brush on a ham during the last 30 minutes of baking time.
Pour remaining 3/4 cup mustard mixture into small saucepan; cook on medium heat until heated through, stirring occasionally.
Serve over ham slices. Use pineapple slices to decorate ham before baking or serve pineapple slices with sliced baked ham.