1. Set dial of temperature controlled burner at 225°F. Combine brown sugar, cornstarch, and allspice in a saucepan.
2. Gradually add the next three ingredients and stir. Cook until sauce thickens and boils.
3. Place one slice of ham in greased baking dish. Pour one half of the sauce over the ham slice. Top with second slice. Add remaining sauce.
4. Bake, covered in 350°F oven for 45 minutes.