POSITION rack in lower third of oven. Preheat to 325F. Slice off and discard any ham rind and netting, if needed. Place ham, fat-side up, in a 9 × 13-in. baking dish. Using a sharp knife, score top and sides of ham in a diamond pattern, about ¼ in. deep. Cover with foil and seal to pan edges. Bake 15 min per 500 g, about 1 ½ to 2 hours.
COMBINE pineapple juice, sugar, ginger and soy in a medium saucepan. Boil over medium-high, stirring occasionally, until syrupy and reduced to 1 cup, 30 to 35 min. Discard ginger. Remove from heat and whisk in butter and Dijon.
REMOVE foil and brush ham with a quarter of the glaze. Continue baking, brushing with glaze every 15 min, until a digital thermo-meter inserted into thickest part of ham registers 140F, about 45 min. Let stand 10 min before slicing. Serve with remaining glaze.