Sift together first 5 ingredients in a large bowl. Whisk together buttermilk, egg yolks, lemon zest, and vanilla in a separate bowl; add to flour mixture, and stir just until moistened. Beat egg whites with an electric mixer on high speed until soft peaks form; fold gently into batter.
Heat an electric griddle to 350°F; brush with melted butter. Drop batter by 1/4-cupfuls onto hot griddle; top each with 3 to 4 blackberries. Cook until edges are set and bubbles begin to appear, 2 to 3 minutes. Turn with a wide spatula, and cook until golden brown, 1 minute.