First you will need to mix the butter and sugar together with a mixer for about 2-3 minutes, until light and fluffy. Add the eggs and mix together. Add the Hershey's syrup and the flour and continue to mix until well combined.
Prepare a 9X13 pan by placing parchment paper on the bottom and up the sides of the pan. Bake at 350° for about 35 minutes or until a toothpick inserted in the middle comes out clean. If you want slightly thinner brownies, you can use a 10X15 jelly roll pan instead. If you use a jelly roll pan, only bake for about 25 minutes.
While the brownies are baking, you need to open the Hershey bars and break them up into the little squares. As soon as the brownies are done, turn the oven off and then place the Hershey bar squares all over the top -they don't have to be perfectly lined up but if you are slightly obsessive-compulsive (like me!) then go ahead and put them in straight lines. You want a little bit of space in between each square.
Put the brownies back in the oven for just a minute or two. The Hershey bar squares will still be intact but should look shiny and have that slightly lighter color that indicates they are melted. Use a knife to spread them around until the brownies are evenly coated. I like to eat at least one brownie while the frosting is still warm and melty, but if you let them set for a few hours, the topping does harden a little bit and isn't quite so messy.