• Grease the bottom of a jellyroll pan (10x15 inches), and preheat the oven to 350 degrees.
• Melt the butter in the microwave, then add sugar and mix well.  Add eggs one a time, mixing well after each addition. Add vanilla. Add flour, and stir to combine. Add Hershey's syrup and mix well. Pour batter into the pan, then bake for 30-35 minutes or until a toothpick comes out clean.  Cool for 5-10 minutes before frosting.

Frosting

• While the brownies are cooling, make the frosting.  You don't want to do this step too early, because it will harden to a fudge-like consistency and be really hard to spread.  
• Measure the powdered sugar into a large mixing bowl.  In a large glass measuring cup, or glass bowl (microwave safe), melt the butter, cocoa, and 2 tablespoons of the milk until it comes to a boil. Stir well, then add to the powdered sugar.  Add the vanilla and the rest of the milk, beating with a wooden spoon until the consistency is smooth. Add a little more milk if necessary. When the brownies have cooled 5-10 minutes, spread the frosting evenly over the top.