Preheat oven to 350 degrees. Grease the bottom and lay parchment paper on the bottom of the a 10-inch round pan. For a thinner bar use a 9x13 cake pan.
In a large bowl, add in butter and peanut butter. Mix on medium until well combined.
Add in sugars and mix on medium until light and fluffy.
Add in the eggs and vanilla and mix on low until incorporated.
Sift the flour, baking soda, and salt together in a separate bowl. Add all to the wet ingredients and mix on low until the dough is formed.
Divide the dough in half and place one half in the bowl you used to sift your flour in.
Sift the cocoa powder into the remaining down and mix on low until the cocoa powder is combined. The dough will be a rich brown color.
Add the chocolate/peanut butter dough to the bottom of the prepared pan.
Place the miniature reese's cups randomly into the dough and push down slightly.
Add the remaining peanut butter dough to the pan and flatten out with your palm. Sprinkle sugar on the top of the bar for decoration.
Place in the oven and bake for 35 or until the bar is brown and done. Turn off oven and let cool in it.