01 -
Whisk together flour, cocoa powder, baking soda, and salt in medium bowl.
02 -
Cream butter and sugars until fluffy. Beat in egg and vanilla. Gradually mix in dry ingredients.
03 -
Drop dollops of peanut butter over dough. Gently swirl with knife to create marbled pattern.
04 -
Cover and refrigerate dough for at least 1 hour.
05 -
Preheat oven to 350°F. Scoop dough onto lined sheets. Bake 10-12 minutes until set but soft.
06 -
Let cookies cool 5 minutes on sheet, then transfer to wire rack.