Begin by creaming 1 cup of softened unsalted butter and 1 cup of sugar in a large mixing bowl until light and fluffy, about 3-5 minutes using an electric mixer. Add in a beaten egg and 1 teaspoon of vanilla extract, mixing thoroughly.

In a separate bowl, whisk together 2 ½ cups of all-purpose flour, ½ teaspoon of kosher salt, and 1 teaspoon of baking soda until blended. Gradually incorporate this mixture into the butter mixture, stirring until the dough comes together smoothly.

Divide the prepared dough into three equal portions. Color one portion red with gel food coloring, the second green, and leave the third uncolored. Wrap in plastic wrap and refrigerate for at least 1 hour.

Roll each colored dough portion between sheets of parchment paper into squares, about ¼ inch thick. Stack red on top of green, then uncolored dough on top. Roll tightly into a log, wrap in plastic, and freeze for 1 hour.

Preheat the oven to 350°F (175°C). Slice the chilled log into rounds about ¼ inch thick. Roll edges in red sanding sugar before placing on a parchment-lined baking sheet. Bake for 8-10 minutes until edges are set and lightly golden.

Remove from the oven and let cool on the baking sheet for a few minutes before transferring to wire racks to cool completely.