To prepare sauce, combine the first 5 ingredients in a small saucepan over medium heat, and stir with a whisk. Add grapes to pan; bring to a boil. Reduce heat, and simmer 1 minute or until slightly thickened. Stir in the blackberries. Remove from heat, and keep warm.
To prepare hotcakes, lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (through salt) in a large bowl, stirring with a whisk. Combine buttermilk and remaining ingredients except cooking spray; add to flour mixture, stirring until smooth.
Pour about 1/4 cup batter onto a hot nonstick griddle or nonstick skillet coated with cooking spray. Cook 2 minutes or until tops are covered with bubbles and edges looked cooked. Carefully turn pancakes over; cook for 2 minutes or until bottoms are lightly browned. Repeat procedure with remaining batter. Serve hotcakes with sauce.