Stir together first 6 ingredients in a large bowl. Cut butter into flour mixture with a pastry blender until crumbly; add buttermilk and sour cream, stirring just until dry ingredients are moistened. Turn dough out onto a lightly floured surface; knead 4 or 5 times.
Pat or roll dough to 3/4" thickness; cut with a 2 1/4" biscuit cutter, and place on a lightly greased baking sheet.
Bake at 425° for 10 minutes. Serve with Sage Butter.