Preheat the oven to 425ºF (220ºC). Line a small rimmed baking pan with parchment paper.
Add the peaches and 3 tablespoons sugar to the small heatproof pan. Toss to combine. Bake until sticky & fragrant, 8 to 10 minutes.
Add the flour, remaining sugar, baking powder, and salt to a medium bowl. Whisk to combine. Scatter the butter over the flour mixture, and rub together quickly with your fingers, until it forms a sandy-looking texture with some pebble-sized pieces.
Using a fork, lightly beat the egg yolk and 3 tablespoons of cream together in a small bowl. Pour over the flour-butter mixture. Add the roasted peaches, and use a wooden spoon to stir together until it forms a crumbly looking mixture.
Knead the dough in the bowl once or twice until it forms a shaggy looking dough.
Turn the dough out onto a lightly floured counter. Knead it once or twice to give the dough a smoother appearance. Using your fingertips, press the dough out into a 1/2-inch thick rectangle. Cut the dough into 4 triangles.
Place the scones on the prepared baking sheet, and brush with tops with the remaining teaspoon of cream. Sprinkle a bit of coarse sugar on top, if desired.
Bake 12 to 14 minutes, until bottoms are deep golden and the tops are golden. Remove from oven and rest tray on a wire rack. Let cool a few minutes before serving.