Preheat the oven to 425 degrees.
In the bowl of a large food processor fitted with a metal blade, process the flour, 1 cup of the sugar, baking powder and salt for about 30 seconds. Cut the butter into ½-inch cubes and add it to the flour mixture. Pulse about 15 times until the butter-flour mixture is crumbly. With the food processor running, slowly pour 1½ cups buttermilk through the feed tube. Stop the processor as soon as the buttermilk has been added. If the dough has begun to stick together in a ball, remove it. If not, add more buttermilk, 1 Tbsp at a time, and pulse until the dough begins to clump up and form a ball.
Place the dough on a lightly-floured flat surface. Use your hands to pat the dough into a ¼-inch thick rectangle, about 12 inches by 10 inches. Spread a thin layer of jam lengthwise over half the dough and arrange the peach slices in a single layer on top of the jam. Fold the plain dough over the peaches to make a 12-inch-by-5-inch rectangle with the jam and peaches folded inside. Cut the dough into 8 triangles and sprinkle the scones' tops with the ¼ cup sugar.
Bake on an ungreased baking sheet for 10 to 15 minutes, until the scones are a light golden brown. Serve warm or at room temperature. Makes 8 large scones.
— Rebecca Rather, chef-owner, Rather Sweet Bakery, from her book The Pastry Queen: Royally Good Recipes from the Texas Hill Country’s Rather Sweet Bakery & Cafe.