Whisk together blackberry mixture, place on the stove, and let it come to a boil. In a separate dish, whisk together your thickener. Once the blackberry mixture is boiling, add the thickener. Then turn down to a medium boil, stirring for 2 minutes. Serve sauce over cut ham slices or as a side to your ham.
Notes
You can also use this sauce as a baste. Pour some of the sauce over the ham and bake according to directions. Baste every 20 minutes till done.