Heat oven to 400°F and line a large baking sheet with parchment.
Whisk flour, oats, brown sugar, baking powder, baking soda, cinnamon, and salt in a large bowl.
Cut in the cold butter with a pastry cutter until the mixture looks like coarse crumbs.
Fold in the raisins until evenly dispersed.
Stir buttermilk and vanilla together, then drizzle over the dry mixture.
Mix gently with a fork just until a shaggy dough forms; do not overwork.
Turn dough onto a lightly floured surface and pat into an 8-inch round about 1 inch thick.
Cut into 8 wedges and transfer to the prepared sheet, spacing the pieces apart.
Brush tops with milk and sprinkle with turbinado sugar.
Bake 15–18 minutes until golden at the edges and set in the centers.
Cool on the pan for 10 minutes before serving warm.