• In a bowl, whisk together the flour, cornstarch and salt. Set aside.
• In another large bowl, beat the butter and sugar on high speed until creamy using a hand mixer or a stand mixer, about 2-3 minutes.
• Add the egg and vanilla and beat for another minute, scraping the sides of the bowl if necessary to fully combine.
• Slowly add the flour mixture to the egg mixture and mix on low speed until thoroughly combined and the dough forms. If the dough is too wet, add a little more flour, a tablespoon a time, until it comes together. It’s perfect when you are able to pick up the dough in one piece.
• Divide the dough in half. 
• Using a toothpick, add a tiny amount of food coloring (if using) to one half of the dough and knead by hand until the dough is fully colored.
• Roll out each batch of dough between 2 sheets of parchment paper to your desired thickness (I roll out mine about ¼ inch / 0.5 cm thick).
• Put the dough in the freezer for 15 minutes.
• Cut each batch of dough into ½ inch (1 cm) strips.
• For one batch of dough, slightly separate the strips by quickly pushing a knife left & right in between each cut to create tiny gaps. Put the dough in the freezer again for 10 minutes.
• Meanwhile, preheat the oven to 350°F / 175°C.

Make the lattice (see the picture tutorial in the post)

• Starting from the center, fold back every second strip of dough.
• Take a strip from the other batch and place it in the center.
• Fold the strips back down to cover the middle strip.
• Fold back the strips that weren't previously used.
• Add another strip of dough and repeat the process until you have a complete lattice.
• Pinch the dough to fix any tears or rips.
• Cut out the cookies with a cookie cutter.
• Remove all the excess dough.
• Re-roll the scraps for marbled cookies and cut them out.
• Transfer the cookies to a baking sheet.
• Bake for about 10 minutes, or until the edges are light brown.
• When done, allow the cookies to cool on the baking sheet for a few minutes before transferring them on to a wire rack to cool completely.
• Store in an air-tight container at room temperature for about 5 days.
• Enjoy!