Preheat oven to 450°. In a large bowl, whisk the first 7 ingredients. Cut in cold butter until mixture resembles coarse crumbs; stir in cheese. Add milk and sour cream; stir just until moistened., Drop by 1/4 cupfuls 2 in. apart onto greased baking sheets. Mix topping ingredients; brush over tops. Bake until light brown, 12-15 minutes. Serve warm.