Making your own you have control over what you put into it. You can make these vegan or gluten free.
Gluten Free: Use a different flour, gluten free, brown rice, almond, etc.
Vegan: Don't put the eggs in, you can use ground chia seeds to replace the eggs.
3/4 cup flour (your choice, try mixing)
1/3 cup bakers cocoa
1 tsp. baking powder
1/2 tsp. baking soda
1/2 cup sugar (if you are adding Oreos, chocolate chips that will already make it sweet so you don't need more sugar, even 1/4 would probably be ok)
1/2 tsp. salt
1/3 cup oil
1 tsp. vanilla
1/2 bag chocolate chips
**Optional: more chocolate chips, oreos, candy of some kind.
Bake at 375 for 20 minutes. (I like using my clay baking pan so they cook more evenly instead of the middle taking longer to cook.)