Step 1

Preparation Preheat oven to 350°F. Toast caraway seeds in a small dry skillet over medium-high heat, tossing occasionally, until fragrant, about 2 minutes. Coarsely chop; set aside.

Step 2

Using an electric mixer on medium-high speed, beat butter, granulated sugar, powdered sugar, and salt until very light and fluffy, 7–10 minutes (beating air into butter makes for tender shortbread). Reduce speed to low and add flour, caraway, and 2 teaspoons chopped rosemary; mix just to combine. Dough will look shaggy and a little dry (it's not!).

Step 3

Press dough into two 8"-diameter cake pans. Brush with egg, sprinkle with sanding sugar, and top with rosemary leaves.

Step 4

Bake until shortbread is golden brown and sides pull away from pan, 20–25 minutes. Transfer pan to a wire rack; let cool in pan before turning out and cutting into wedges or bars.

Step 5

MAKE AHEAD: Shortbread dough can be made 1 month ahead; wrap tightly and freeze. Shortbread can be baked 1 week ahead; store wrapped tightly at room temperature.