Heat the oven to 425°F (218°C) then dice butter into rough ½-inch cubes and put it in the freezer while you make the filling.

Cut peaches into roughly 2-inch chunks. Toss them with 60g granulated sugar, 60g brown sugar, and 4g salt, then let stand for 5 minutes.

Transfer peaches and their liquid to a saucepan. Cook over medium-high, stirring occasionally, until the peaches begin to soften and peach liquid reduces by about half, 5–10 minutes.

Stir together cornstarch and water then stream the slurry into the simmering peaches while stirring constantly. Bring to a full boil and cook 1 minute until thickened. Remove from heat and stir in lemon juice and vanilla.

Pour filling into an oiled 12” cast iron pan and set aside to cool while you make the biscuit topping.

Add 145g sugar, flour, baking soda, baking powder, and 7g salt to a food processor. Pulse to combine. Add the frozen butter, and pulse in short bursts until the mixture looks like fine gravel with small irregular lentil sized butter pieces still visible.

Move the butter-flour mixture to a mixing bowl, add buttermilk, and toss gently with a fork or just until no loose flour remains.

Drop the dough over the filling in 10–11 tall mounds, about 50–60g each, leaving roughly 2 inches between them. Sprinkle each dough mound with demerara sugar.

Bake at 425°F (218°C) with convection off for 25–28 minutes, until the biscuits are deeply golden, set in the center, and the filling is bubbling hard between them.

Cool for 45 minutes. Top with a scoop of vanilla ice cream and serve while the fruit is still warm and the biscuit tops are crisp.