Preheat oven to 350°F. Cream the unsalted butter and sugar in a stand mixer until light and fluffy.

Add the egg and vanilla extract to the mixture and combine until smooth.

In a separate bowl, whisk together flour, kosher salt, and baking soda. Gradually mix into wet ingredients until combined.

Divide the dough into three portions, color one red, one green, and leave one uncolored. Wrap in plastic and refrigerate for 1 hour.

Roll each colored dough into 7-inch squares between parchment paper, then chill for an additional 15 minutes.

Stack the dough in the order of red, green, and plain, then tightly roll into a log and freeze for 1 hour.

Slice the log into 1/3-inch thick rounds and roll edges in red sanding sugar before placing on a baking sheet.

Bake for 8-10 minutes, allowing cookies to remain soft and chewy, then cool on a wire rack.