Score ham in diamond pattern, if desired. Place on rack in a shallow roasting pan. Bake, uncovered, in 325 degree F. oven for 1-3/4 hours. Meanwhile, in small saucepan, blend wine and lemon juice into cornstarch. Add about half of the jam. Cook and stir until thickened and bubbly. Stir in remaining jam and butter. Heat and stir until butter is melted.