If your blackberries are particularly sweet or tart, adjust the amount of sugar in the sauce accordingly by 1/2 teaspoon or so to find the right balance.
2 tablespoons minced shallots
3 cups fresh blackberries (about 1 pound)
1/2 teaspoon chopped fresh sage
1 (14-ounce) can fat-free, less-sodium chicken broth
2 tablespoons balsamic vinegar
1 1/2 teaspoons sugar
1 tablespoon butter
3/4 teaspoon kosher salt, divided
1 teaspoon black pepper
1 (1 1/2-pound) pork tenderloin, trimmed
Sage sprigs (optional)
How to Make It
Prepare grill to medium heat.
Heat a medium saucepan over medium heat. Coat pan with cooking spray. Add shallots to pan; cook 3 minutes or until tender, stirring occasionally. Add blackberries, sage, and broth; bring to a boil. Reduce heat, and simmer 20 minutes or until blackberries break down. Press blackberry mixture through a fine sieve over a bowl; discard solids. Return liquid to pan. Stir in vinegar and sugar; bring to a boil. Cook until reduced to 3/4 cup (about 9 minutes); remove from heat. Stir in butter and 1/4 teaspoon salt, stirring until butter melts. Keep warm.
Sprinkle remaining 1/2 teaspoon salt and pepper over pork. Place pork on grill rack coated with cooking spray; cover and grill 20 minutes or until a thermometer registers 155° (slightly pink), turning pork occasionally. Let stand 10 minutes. Cut crosswise into 1/4-inch-thick slices. Serve with blackberry sauce; garnish with sage sprigs, if desired.