Chocolate Shortbread Fingers

Step 1

Preheat the oven to 325°F. Butter a 12-by-8-inch rimmed baking sheet, and line with parchment paper, leaving a 1-inch overhang on long sides; set aside. In a medium bowl, whisk together flour, cocoa, cinnamon, salt, and baking soda until combined.

Step 2

In an electric mixer fitted with the paddle attachment, beat the butter and superfine sugar on medium-high speed until light and fluffy, 3 to 4 minutes, scraping down the sides of the bowl. Add flour mixture, and beat on medium speed until just combined.

Step 3

Using a small offset spatula, evenly spread dough in prepared baking sheet. Chill in the freezer or refrigerator until dough is firm, about 15 minutes. Prick dough all over with a fork; bake until just firm to the touch, about 20 minutes. Transfer to a wire rack. While still hot, use a large knife to cut shortbread into 4-by-1-inch pieces. Sprinkle with granulated sugar. Cool completely in the pan. Shortbread can be kept in an airtight container at room temperature for up to 1 week.