Preheat and prepare your dish. Set your oven to 190°C (170°C fan) and generously butter a 23cm x 23cm baking dish or a 25cm cast-iron skillet. You should hear a faint sizzle as the butter melts against the warm dish later.

Prepare the peaches. Bring a large saucepan of water to a rolling boil. Gently lower the peaches in for 30–40 seconds, then transfer them to a bowl of ice water. The skins will slip off easily. Cut each peach in half, remove the stone, and slice into 2cm-thick wedges. You should have roughly 900g of sliced fruit.

Sauté the filling. In a large frying pan over medium-high heat, combine the sliced peaches, caster sugar, and a pinch of salt. Cook for 6–8 minutes, stirring occasionally. You’ll see the peaches release their juices, which will then start to bubble and thicken into a syrupy glaze. The fruit will turn from opaque to semi-translucent and will smell intensely sweet and floral.

Thicken the glaze. In a small bowl, whisk the cornflour with the lemon juice until smooth. Pour this slurry into the pan with the peaches and stir constantly for 1 minute. The mixture will immediately go from a thin syrup to a glossy, jammy consistency that coats the back of a spoon. Stir in the vanilla and cinnamon, then remove from the heat. The colour should be a deep, burnished gold.

Make the cobbler topping. In a large mixing bowl, whisk together the plain flour, granulated sugar, baking powder, and bicarbonate of soda. Create a well in the centre and pour in the buttermilk and the melted butter. Stir with a wooden spoon just until a soft, shaggy dough forms. Do not overmix—a few dry patches are perfectly fine. The dough will be quite wet and sticky, which is what you want for a tender result.

Assemble the cobbler. Pour the warm peach filling into your prepared dish and spread it into an even layer. Using two spoons, drop heaped spoonfuls of the dough over the top of the filling. Don't smooth it out; leave rough, craggy peaks—these will become wonderfully crisp. Sprinkle the demerara sugar evenly over the dough lumps.

Bake to golden perfection. Place the dish on a baking tray to catch any bubbling juices. Bake for 35–45 minutes, until the topping is deep golden brown and the filling is bubbling up around the edges with thick, syrupy bubbles. You’ll hear it gently hissing as it bakes. A skewer inserted into the thickest part of the topping should come out clean. Let it rest on a wire rack for 15 minutes—this allows the juices to settle and thicken further.