These Italian cookies are made without butter or oil and are twice baked to crisp perfection. Try Almond Biscotti, Cherry Espresso Biscotti, Rum-Soaked Raisin Biscotti, and Brown Sugar and Date Biscotti.
Preheat oven to 350 degrees. In a large bowl, whisk together flour, cocoa powder, cayenne, cinnamon, sugar, baking powder, and salt. Using an electric mixer, beat in eggs and vanilla until combined. Add bittersweet chocolate and beat until combined.
Divide dough in half and transfer to a parchment-lined rimmed baking sheet. Form each half into a 2 1/2-inch-wide, 3/4-inch-tall log. Bake until dough is firm but gives slightly when pressed, 20 to 25 minutes, rotating sheet halfway through. Let cool on sheet on a wire rack, 20 minutes.
With a serrated knife, cut logs into 1/4-inch slices on the diagonal and arrange, cut side down, on two parchment-lined rimmed baking sheets. Bake until biscotti are crisp and golden, about 15 minutes, rotating sheets and flipping biscotti halfway through. Let cool on sheets on wire racks.
The dough can be sticky, so lightly flour your hands or coat them with cooking spray before shaping it into logs. Making the logs as uniform as possible ensures even baking.
Store in an airtight container, up to 2 days, or freeze, up to 3 months.