Mix wet ingredients In a bowl, mix brown sugar, sugar, melted butter, egg, vanilla, and milk until smooth.

Add dry ingredients Add flour, salt, baking soda, baking powder, cornstarch, and cocoa powder. Mix just until combined.

Add mix-ins Fold in pecans, marshmallows, and chocolate chips.

Chill dough Refrigerate dough for at least 30 minutes.

Bake Bake at 350°F (177°C) for 12 minutes.

Cool slightly Let sit on tray a few minutes before moving so marshmallows don’t tear.