Preheat oven to 450º convection, 475º conventional
Whisk dry ingredients together in a large bowl. Add vanilla to buttermilk.
Drop in cold butter cubes and work in with your fingers until shaggy and butter shards are about dime-sized. Pour in most of cold buttermilk and fold in with spatula. If it seems dry, add the rest and stir a few more times.
Dump onto a floured surface and knead gently about three times and pat into a rough 1/2" thick rectangle. Using a rolling pin, gently roll into a 12" x 10" rectangle. Scatter blueberries over the top leaving a 3/4" border (I left closer to an inch and had blueberry-less rolls on the ends). Sprinkle about one tablespoon of raw sugar over the berries. Roll towards yourself being careful not to compress it too much. Pinch seam so it stays shut. Brush roll with melted butter and roll in remaining raw sugar. Cut roll into one inch pieces and place face up on an ungreased sheet pan. Bake for 12 minutes or until brown and bubbly. Cool completely.