These little cookies are easy to bake and look super fun, perfect for a baking with children.
In a bowl, stir together flour, baking powder, and salt. In a separate large bowl, beat butter and sugar with electric mixer until light and fluffy, about 2 minutes. Add the eggs, one at a time, beating after each addition; add vanilla. Add the flour mixture and beat on low until just combined.
Divide dough in half. Form one half into 4 in. by 4 in. square; wrap in cling film and set aside. Return other half to the mixer; add melted chocolate to dough and beat just until combined. Form the chocolate dough into 4 in. by 4 in. square and wrap in cling film. Refrigerate both doughs for at least 30 minutes.
On parchment paper, roll the vanilla dough into a 16 in. x 12 in. rectangle about 1/8 in. thick. On another sheet of parchment paper, roll chocolate dough into a 16 in. x 12 in. rectangle about 1/8 in. thick.
Place chocolate dough on top of the vanilla dough; peel away parchment. Cut dough horizontally in half. Roll each half into a tight log. Roll in coloured sugar to coat. Wrap in cling film and refrigerate for 3 hours or overnight.
Preheat the oven to 350 °F. Line cookie sheets with parchment paper.
Slice logs in to ¼ in pieces. Space 1 in. apart on the cookie sheet. Bake for 8-10 minutes or until the vanilla dough is lightly golden.