In a large mixing bowl, combine 1 cup of softened unsalted butter and 1 cup of granulated sugar. Cream together for about 3-5 minutes until light and fluffy.

Crack one large egg into the bowl and mix on low speed until just combined. Ensure all ingredients are incorporated.

In a separate bowl, whisk together 3 cups of all-purpose flour and ¼ cup of cocoa powder. Gradually add into wet ingredients, mixing on low speed.

Divide the dough into two equal portions. Keep one portion plain and knead an additional ½ cup of cocoa powder into the other.

Prepare a baking sheet lined with parchment paper. Alternately place small portions of both doughs on the sheet, spaced about 2 inches apart.

Use a toothpick or skewer to swirl the dough to create zebra patterns.

Preheat oven to 350°F (175°C) and bake for 10-12 minutes until edges are lightly golden.

Allow cookies to cool on the baking sheet for about 5 minutes before transferring to a wire rack.