3/4cup1 1/2 sticks chilled unsalted butter, cut into 1/4" cubes
1cupplus 2 tablespoons buttermilk
2teaspoonsfinely grated lemon zest
2tablespoonssanding or granulated sugar
1 1/2cupsstore-bought lemon curd
Arrange racks in upper and lower thirds of the oven; preheat to 425°F. Line 2 baking sheets with parchment paper. Whisk 3 cups flour and next 5 ingredients in a large bowl. Add butter; rub in with your fingers until mixture resembles coarse meal.
Whisk 1 cup buttermilk, zest, and vanilla in a small bowl. Add wet ingredients to dry ingredients. Stir until shaggy dough forms.
Transfer to a lightly floured surface; knead until dough forms, about 5 turns. Pat into a 10x6" rectangle. Halve dough lengthwise. Cut each half crosswise into 4 squares. Cut each square diagonally in half into 2 triangles. Divide between baking sheets. Brush with 2 tablespoons buttermilk. Sprinkle with sanding sugar.
Bake until scones are golden and a tester inserted into the center comes out clean 13-15 minutes. Transfer to wire racks; let cool. Serve warm or at room temperature with lemon curd.
Dried lavender buds (culinary lavender) are available at some supermarkets and natural foods stores.