Preheat oven to 400. In a food processor, pulse together flour, cup sugar, baking powder, and salt. Add butter and pulse until pea-size pieces form. In a small bowl, whisk together buttermilk and egg yolk. Slowly pour buttermilk mixture through feed tube into processor, pulsing until dough just comes together.
Transfer dough to a lightly floured work surface and sprinkle raspberries on top. Knead three times to fold in raspberries (there may be loose pieces of dough and a stray berry or two). Gather and pat dough into a 1-inch-thick square and cut or pull apart into 2-inch pieces. Place pieces, about 2 inches apart, on two parchment-lined rimmed baking sheets and sprinkle tops with 1 tablespoon sugar.
Bake until golden brown, 15 to 18 minutes, rotating sheets halfway through. Let scones cool slightly on sheets on wire racks. Serve warm or at room temperature.
Store in an airtight container, up to 1 day.