Spread the desired amount of prepared frosting on the completely cooled brownies.
Place the frosted brownie layer in the refrigerator or freezer for a bit to solidify the frosting on top.
When the frosting is cool on top and set, microwave the 3 cups of chocolate chips for 45 seconds at a time, stirring between heating. Take your time with this and stir well so you don't ruin the chocolate by overheating it.
When the chocolate is just melted, pour it over the frosting as shown in the photo.
Using the back of a spoon, spread the chocolate around on top and cover the frosting. Work quickly, so frosting doesn't melt underneath.
Let the chocolate layer set for half an hour, and then score it for easy cutting later. I scored mine 9 bars by 11 bars for 99 bars.
When brownies are completely set, cut. I like to put mine in the fridge for another half hour to make cutting easier and tidier.
Serve or freeze for later. These freeze well.