Grilled Pork with Blackberry-Sage Sauce

If your blackberries are particularly sweet or tart, add about 1/2 teaspoon of sugar to the sauce to find the right balance.
Cook the grill over medium heat.Preheat a medium saucepan over medium-high heat. Brush the mold with cooking spray. Add the shallots to the skillet; cook for 3 minutes or until tender, stirring occasionally. Add the blackberries, sage, and stock; bring to a boil. Reduce the heat and simmer for 20 minutes or until the blackberries are cooked through. Rub the blackberry mixture through a fine sieve over a bowl; remove any dry residue. Return the liquid to the mold. Add vinegar and sugar; bring to a boil. Cook until reduced to 3/4 cup (about 9 minutes); remove from heat. Add the butter and 1/4 teaspoon salt, stirring until the butter melts. Keep warm.Sprinkle the pork with the remaining 1/2 teaspoon salt and pepper. Place the pork on a grill rack greased with cooking spray; cover and cook for 20 minutes or until the thermometer reads 155 ° (slightly pink), turning the pork occasionally. Let stand for 10 minutes. Cut crosswise into 1/4-inch thick slices. Serve with blackberry sauce; garnish with sage sprigs if desired.