Preheat the oven to 350F.

Butter a 9x13-inch baking dish; set aside.

In a large bowl, toss together peaches, 3/4 cup of the granulated sugar, cornstarch, vanilla, 1/2 teaspoon of the salt and cinnamon; set aside.

In a food processor, pulse flour, remaining 1/4 cup granulated sugar, baking powder and remaining 1/2 teaspoon salt until combined.

Add shortening and 8 tbsp of the butter, and pulse until pea-sized lumps remain.

Add buttermilk and pulse again, just until mixture forms a rough dough.

Stir peach mixture well, then transfer to prepared dish.

Drop dough onto peaches in large dollops.

Melt remaining 2 tablespoons butter and brush onto dough, then sprinkle all over with turbinado sugar.

Bake until peaches are tender and bubbly and biscuits are puffed and golden brown, about 1 hour.

Serve warm or at room temperature.