I got this recipe off the www.hersheys.com site and they are fabulous. I love doing new recipes and having them be great just like they are - and then they go in that permanent recipe folder - these are them!
3 sticks butter, melted
3 cups sugar
1 tbsp vanilla (you could put mint extract in here if you want it more minty)
2 cups flour
1 cup cocoa powder
1 tsp baking powder
1 tsp salt
24 regular size york peppermint patties
325 (glass pan, 350 normal pan). Grease pan 13x9. Cream butter, sugar and extract. Add eggs one at a time. Add dry ingredients. When all mixed together, reserve two cups of batter. Pour in rest of batter in pan, layer with 24 york patties, then spread the 2 cups remainder over the top. Bake for 65 minutes or until done. Let cool overnight - makes them easier to cut.
Enjoy - I saved some of the crumbs and little bits for ice cream topping - yummy!