Here's the thing about brownies. You mustn't overcook them. They're not cake. They're meant to be gooey. Also, although it's possible to add too many chocolate chips, I've yet to see it happen in my kitchen. Lastly, to bake in cast iron is divine.
Assuming you're cooking with real ingredients and/or have a high-quality mix, they shouldn't stick to cast iron. The directions on the extremely yummy Dassant chocolate chip brownies (they taste like homemade because they have awesome ingredients–for real, read the label!) call for parchment paper and greasing the pan. Ha! I lift my chin in disdain at your parchment paper!
Preheat the oven with your super-awesome 8" round cast iron pan in the oven. Mix the brownies according to the recipe. Add chocolate chips, or butterscotch chips, or white chocolate chips, if desired. When the oven is preheated, remove the cast iron pan and carefully pour (or rather scrape and shovel) the brownie mix into the hot pan. The sides will rise much more than the center. Don't be alarmed. It will still tasted good. Check the brownies earlier than the directions say, as the hot pan may cook them faster than the directions state. When the center no longer wiggles like jello and a toothpick inserted comes out only slightly goopy with mix (most likely it's melted chocolate chips anyway), remove from the oven and allow to cool for as long as you can stand it.
Ice cream is not amiss in such situations.
This is how your pan should look when you remove the still-warm brownies:
|Notice the lack of brownie stuck to the pan|
Should the brownies for some reason stick a bit to the pan, run the pan under hot water. The residue should slough right off.
Cast iron is amazing. Love your cast iron pans, and they'll love you right back.