Mix the wet ingredients: Whisk together the vanilla, egg, butter, brown sugar and granulated sugar.
Add the dry ingredients: Add the flour, baking powder, and salt. Mix until a dough forms, then fold in the chocolate chips.
Shape the dough: Place the dough between two sheets of parchment. Roll into a rectangle roughly 16.5 × 20 cm (6.5 × 8 inches), about 0.6 cm (1/4 inch) thick. Press extra chocolate chips on top if you like.
Chill: Slide the dough (on the parchment) onto a tray and freeze for 10 minutes. Cut into long “fries” (10–12 pieces). Space them out on a lined tray and freeze again for 30–60 minutes, don’t skip this!
Bake: Preheat oven to 180°C (350°F). Bake for 14–16 minutes, rotating the tray halfway, until lightly golden at the edges.
Cool: Let them firm up on the tray for 10 minutes, then move to a wire rack. Serve as they are or with chocolate sauce for dipping.