In a large mixing bowl, beat the butter and sugar until light and creamy (about 3-4 minutes).

Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.

Sift the flour, salt, and baking powder over the butter mixture and stir until combined.

Divide the dough into three equal portions. You will add color to two of them and leave one portion uncolored.

Knead the red gel food coloring into one portion until evenly colored. Repeat with the green gel food coloring for another portion.

Roll each portion of dough into a 14 x 8-inch rectangle on a lightly floured surface. I roll them out between sheets of waxed paper for easy handling.

Layer the rectangles on top of each other. Gently press the layers together to eliminate air pockets. If the sheets of dough are too soft to move and stack easily, chill them in the refrigerator for about 10 minutes to firm up.

Starting with one of the long edges, tightly roll the stacked dough into a log, similar to a jelly roll. Use parchment paper or waxed to guide the dough as you roll.

Roll the outside of the log in sparkling sugar, pressing gently to help the sugar stick.

Wrap the log tightly in plastic wrap and chill in the freezer for 30-45 minutes, or until firm.

Preheat your oven to 350°F. Line baking sheets with parchment paper or a silicone baking sheet.

Remove the chilled dough from the freezer and slice into ¼-inch thick rounds using a sharp knife.

Arrange the slices on the prepared baking sheets, leaving about 1 inch between each cookie.

Bake for 9-11 minutes, or until the edges are just barely golden.

Let the cookies cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.