Instructions

1. In a medium bowl, whisk together the all-purpose flour, baking soda, and salt until well combined. Set aside.
2. In a large mixing bowl, cream the softened butter and granulated sugar together using an electric mixer until light and fluffy, approximately 3-4 minutes.
3. Add the egg to the butter mixture and beat until fully incorporated, scraping down the sides of the bowl as needed.
4. Gradually add the dry flour mixture to the wet ingredients, mixing on low speed until a smooth dough forms.
5. Divide the cookie dough into 5 equal portions, placing each in separate small bowls.
6. Add a different food coloring to each dough portion: red, orange, yellow, green, and blue. Mix thoroughly until each portion is evenly colored.
7. On a piece of plastic wrap, layer the colored dough portions one on top of another, pressing gently to create a rainbow-like stack.
8. Wrap the dough tightly in plastic wrap, forming a log shape. Refrigerate for at least 2 hours or overnight to firm up.
9. Preheat the oven to 350°F (175°C) and line two baking sheets with parchment paper.
10. Remove the dough log from the refrigerator and unwrap. Using a sharp knife, slice the log into 1/4-inch thick rounds.
11. Place the cookie rounds on the prepared baking sheets, spacing them about 2 inches apart.
12. Bake for 10-12 minutes, or until the edges are lightly golden brown.
13. Remove from the oven and let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
14. Store cookies in an airtight container at room temperature for up to 5 days.