Preheat the oven to 350 degrees F. Put oven rack in the middle of the oven.
In a small bowl, mix together the Dijon mustard, brown sugar, and thyme.
Put the ham in a large roasting pan, fat side up. Rub the ham with mustard glaze. Pour the pineapple juice into the bottom of the pan. Put the ham in the oven and bake for 2 hours, brushing every 20 minutes with the pineapple juice. Remove the ham from the oven.
Turn oven to 400 degrees F.
Using toothpicks, decoratively adhere the pineapple rings around the ham and put a cherry in the center of the pineapple ring. Sprinkle the pineapple rings lightly with brown sugar. Return to the oven, uncovered, and bake until the pineapples turn a light golden brown. Remove from the oven to a serving platter and let rest for 15 minutes before slicing.