01 -
Whisk flour, cocoa, baking soda and salt in a bowl.
02 -
Beat butter and sugar 3-4 minutes until fluffy.
03 -
Beat in eggs one at a time, then vanilla.
04 -
Mix in dry ingredients just until combined. Can swirl in marshmallow now or later.
05 -
Cover and chill dough at least 1 hour.
06 -
Scoop dough balls, make indent, add marshmallow and swirl with toothpick.
07 -
Cook at 350°F for 10-12 minutes until edges set but centers soft.
08 -
Let rest 5 minutes on pan, then move to rack to cool fully.