Spoon on the jam and spread the butter -- these orange-poppy scones are ideal for a Mother's Day brunch.
Preheat oven to 400 degrees, with racks in upper and lower thirds. In a large bowl, whisk together flour, granulated sugar, baking powder, and salt. With a pastry blender or your fingertips, work butter into flour mixture until mixture resembles coarse meal, with a few pea-size pieces of butter remaining. With a fork, stir in 1/2 cup buttermilk, orange zest and juice, egg yolk, and poppy seeds until just combined.
On a lightly floured surface, turn out dough and knead several times. Form dough into a 7-inch square; cut into 9 squares, then cut each in half diagonally. Transfer dough triangles to 2 parchment-lined rimmed baking sheets. Brush tops with 2 tablespoons buttermilk; sprinkle with coarse sugar. Bake until scones are pale golden, 15 to 17 minutes, rotating sheets halfway through. Let cool on wire racks. Serve with butter and jam, if desired.
Store scones in an airtight container, up to 3 days. Warm in oven before serving.