4 1/2 pounds freestone peaches—peeled, pitted and diced (10 cups)
2 1/2 tablespoons instant tapioca
1/3 cup sugar
1/2 teaspoon kosher salt
1/2 teaspoon fresh lemon juice
1 teaspoon dried lavender blossoms
1 cup all-purpose flour
1/2 cup plus 2 tablespoons rolled oats
1/4 cup granulated sugar
1 tablespoon baking powder
1 1/4 teaspoons kosher salt
Finely grated zest of 1 lemon
5 tablespoons unsalted butter, diced
1/2 cup heavy cream, plus more for brushing
1/4 cup buttermilk
2 tablespoons turbinado sugar
Preheat the oven to 400°. In a bowl, mix the peaches, tapioca, sugar, salt and lemon juice. Transfer the filling to a 9-by-13-inch baking dish.
Using a spice grinder or a mortar and pestle, grind the lavender to a powder. In a bowl, combine the lavender, flour, oats, granulated sugar, baking powder, salt and lemon zest. Cut in the butter using a pastry blender or two knives, until the mixture resembles coarse meal. Add the 1/2 cup of cream and the buttermilk; stir until the dough is just moistened.
Using two spoons, form 3-tablespoon mounds of the topping and arrange them evenly over the peaches. Brush with cream and sprinkle with the turbinado sugar. Bake the cobbler for 50 minutes, until the topping is golden brown and the fruit is bubbling. Let cool slightly before serving.