In a medium mixing bowl, whisk together dry ingredients ( flour, cocoa powder, soda and salt ). Set aside.
Place butter and both sugars in a large mixing bowl of a stand mixer and cream until light and fluffy.
Add egg and vanilla and zest and mix just until combined.
With mixer on low speed, add dry ingredients and mix just until combined. Fold in cereal and chocolate chips.
Cover the dough and refrigerate until thoroughly chilled ( 2 to 3 hours, preferably overnight ).
When ready to bake, preheat your oven to 350 degrees Line your cookies sheet with parchment paper. Scoop out the dough into a tablespoon size balls and place on prepared sheet, leaving at least 2 inches of space between cookie balls. They will spread!
Bake 9 to 11 minutes. Cool on a sheet for 3 minutes, then transfer onto a cooling rack.