Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
Cream butter and sugar until light and fluffy.
Add eggs one at a time, then vanilla extract. Mix until combined.
Whisk together flour, cocoa powder, baking powder, and salt.
Divide dough in half. Add cocoa powder to one half.
Roll chocolate and vanilla doughs into logs of equal size.
Twist the two logs together and cut into ½-inch slices.
Place slices on prepared baking sheet, spacing 2 inches apart.
Bake 10–12 minutes until edges are set but center is soft.
Cool on wire rack before serving.
