In a mixing bowl, cream together 1 cup of softened butter and 1 cup of sugar until light and fluffy, about 3-5 minutes.

Add 1 large egg and 1 teaspoon of pure vanilla extract and mix until fully incorporated.

In a separate bowl, whisk together 2 cups of all-purpose flour, 1/3 cup of cocoa powder, and a pinch of salt. Gradually add this dry mixture to the wet ingredients and mix on low speed.

Divide the dough in half, leaving one half plain and adding 1 tablespoon of cocoa powder to the other half.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Alternate spoonfuls of the vanilla and chocolate dough on the baking sheet.

Use a toothpick or skewer to gently swirl the dollops of dough to create the zebra pattern.

Bake the cookies for 10-12 minutes until the edges are set. The cookies should be soft in the center and firm around the edges.

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