Preheat oven to 350°F (175°C) and prepare a baking sheet with parchment paper.

Cream together 1 cup of softened unsalted butter, ½ cup of granulated sugar, and ½ cup of brown sugar in a mixing bowl.

Incorporate 1 large egg and 1 teaspoon of vanilla extract into the creamed mixture until fully combined.

Mix together 2 cups of all-purpose flour, 1 teaspoon of baking soda, and ¼ teaspoon of salt in a separate bowl.

Gradually add the dry mixture into the wet ingredients, mixing on low speed just until combined.

Divide the dough in half; fold in ½ cup of creamy peanut butter into one half and ½ cup of melted semi-sweet chocolate chips into the other half.

Drop alternating spoonfuls of both doughs onto the baking sheet and swirl gently with a knife or toothpick.

Bake for 10-12 minutes, until edges are lightly golden but centers are slightly soft. Let cool on the baking sheet for a few minutes.

Transfer cookies to a wire rack to cool completely before serving.