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.