In a medium bowl, whisk together 1 cup of all-purpose flour, 1/4 teaspoon of fine salt, 1/2 cup of unsweetened cocoa powder, and 1 teaspoon of baking soda until well blended.

In a large mixing bowl, cream together 1/2 cup of softened butter, 1/2 cup of brown sugar, and 1/2 cup of white sugar until light and fluffy. Beat in one large egg and 1 teaspoon of vanilla extract until smooth.

Gradually incorporate the dry ingredient mixture into the wet ingredients, stirring slowly until combined.

Spoon blobs of 1/2 cup of smooth peanut butter into the dough and gently swirl through the mixture.

Cover the bowl tightly with plastic wrap and chill the dough in the refrigerator for at least one hour.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Drop spoonfuls of the chilled dough onto the sheets.

Bake the cookies for 10-12 minutes; they should appear set but still soft in the centers.

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