- Put the sugar into the blender jug and, with the measuring beaker in place, pulverise for 10 seconds/speed setting 8. Use the spatula to scrape the icing sugar down the inside of the blender jug, and repeat the process if necessary.
- Score the vanilla pod lengthways with a sharp knife and scrape out the pulp with the back of the knife. Put vanilla pulp, flour, baking powder, vanilla sugar, egg and chilled butter in pieces into the blender jug and, with the measuring beaker in place, stir for 40 seconds/speed setting 4.
- Remove half the dough from the blender jug, shape into a ball, wrap in cling film and chill in the refrigerator for 1 hour.
- Pour the cocoa and the milk into the blender jug and, with the measuring beaker in place, stir for 20 seconds/speed setting 4. Shape the dough into a ball, wrap in cling film and also chill in the refrigerator for 1 hour.
- To make a snail pattern:
- Put both balls of dough on a floured surface, roll them out thinly and separately to make rectangles each measuring 30 × 20 cm. Beat the egg white in a small bowl with a fork and brush the light-coloured dough with the egg wash. Place the dark-coloured dough on the egg-washed side of the light-coloured dough, press down lightly and roll up tightly along the long side. Wrap the roll in cling film and chill in the refrigerator for 30 minutes.
- To make a chessboard pattern:
- Beat the egg white in a small bowl with a fork. Put both balls of dough on a floured surface and roll them out to a thickness of 1 cm. Then cut into equally sized strips measuring 1 × 20 cm. Lay 3 strips next to one another, alternating one light and one dark-coloured strip. Brush a thin layer of the beaten egg white on these 3 strips. Place 2 further layers, each consisting of 3 strips on top of the original strips, alternating between a light and a dark-coloured strip.
- Knead the remaining light and dark doughs together, roll out thinly and create an edge around the chessboard block as desired. Wrap the block in cling film and chill in the refrigerator for 30 minutes.
- Pre-heat the oven to 175 °C, and line 2 baking sheets with greaseproof paper. Using a sharp knife, cut 8-mm-thick slices from the ball of dough (when making the snail pattern) or 8-mm-thick slices from the block of dough (when making the chessboard pattern) and place them on the baking sheets. Bake each sheet one after the other for 12 minutes.
- Allow the cookies to cool on a cake rack.
If made for adults only, you can replace the milk with rum.
When kept in a tin, the black-and-white cookies will keep for 4 weeks.
Bon appétit with Monsieur Cuisine