Preparation

1. Preheat oven to 350. Prepare a baking sheet with parchment paper.
2. Cream butter and sugar together in a large bowl. Mix in vanilla, lemon, and salt, stirring to combine.
3. Slowly incorporate flour into the butter mixture. Make sure to scrape down the sides.
4. Place dough on a clean work surface and knead for 1-2 minutes. The dough will be crumbly.
5. Divide dough in half, and sprinkle cocoa powder over one of the halves, kneading until fully incorporated.
6. Place each half of the dough between two sheets of plastic wrap. Shape each half into a 7 inch square, about 1/2 inch thick. With a knife and a ruler, measure and cut out 3/4 inch strips. Each square should yield 9 strips.
7. Make an egg wash by whisking the egg and 1 tablespoon of water together. Lay out a clean sheet of plastic wrap, and place 3 strips of dough on the plastic, alternating colors. Brush with egg wash and press strips together gently. Repeat with more layers, alternating colors, and brushing with egg wash. The dough should make 2 checkerboard logs. Wrap these logs in plastic wrap, and freeze for 15 minutes.
8. Remove logs from freezer and cut 1/4 inch slices. Place on prepared baking sheet and bake for 10-12 minutes.