Preheat the oven to 350 degrees and prepare a baking sheet with parchment.
In a food processor, combine flour, sugar and salt.
Add butter pieces and pulse until dough resembles small crumbles.
Add the vanilla extract and egg yolk. Pulse until the dough comes together.
Transfer dough to a lightly floured service. Shape dough into a round and divide it into four even portions.
Put a small amount of food coloring in the center of one section. Knead the dough until the color is evenly distributed.
Using your hands, work each section of dough into a long rectangle. Place in the fridge for 20 minutes.
Using a knife and a ruler trim the edges to be 1" high, 1" wide, and 9" long.
Place the dough back in the fridge for another 20 minutes.
Press press the strips together to form one large block.
Using a knife, cut dough into 1/4" slices. Bake for 12 -15 minutes.
Remove baking sheet from oven. Let cookies sit for 2 minutes and then transfer to wire rack to cool.