Preheat the oven to 350° F. Grease two 11 X 8 baking pans with butter and line with parchment paper.
Place the butter and sugar in a microwave safe bowl and microwave in 30-second increments, whisking in between. Repeat until butter is melted.
Allow the mixture to cool, then whisk in one egg at a time. Add the cocoa powder, salt, and vanilla extract. Fold in flour and the chocolate chips until just combined. Pour the mixture into the prepared baking pan and bake for 45 minutes. To check for doneness, insert a toothpick into the center of the brownies. Let the brownies cool before slicing into 36 rectangles.
Divide the frosting into 3 small mixing bowls and add a few drops of food coloring to each, mix until fully combined.
Spread the frosting over the top half of each brownie, add candy eyes and let set.