Preheat oven to 350 and line a 12 cup and a 6 cup muffin pan with paper liners.
Mix dry ingredients. Add eggs and oil. Beat on low and slowly add the vanilla, milk, and water. Beat only until all ingredients are incorporated and the batter is smooth. Use an ice cream cup or small ladle to spoon about ¼ cup mixture into each cup.
Unwrap 18 Reese's miniatures and place one into the batter pressing down until the top of the miniature is flush with the top of the batter. Top each muffin cup with an additional tablespoon of batter to cover the Reese's cups. Smooth with the back of a spoon to make sure the batter is distributed evenly.
Bake for 20 minutes or until tops are rounded and centers are set.
To make icing, pour excess oil off of peanut butter. Stir remaining peanut butter until well mixed. I find it helpful to pour the whole jar into a separate container and stir it that way.
Add the stick of butter, one cup of the peanut butter one cup of the powdered sugar and one tablespoon of the half and half. Beat slowly at first then on medium speed until well mixed. Scrape down the sides of the bowl then keep adding the sugar a ½ cup at a time and the half and half a tablespoon at a time. You can add more half and half for a creamier texture and more sugar for stiffer icing.
Place icing in a piping bag and ice cupcakes or spread on with a knife or spatula. Take 9 remaining Reeses Miniatures and cut them in half. Place half a miniature on top of each iced cupcake.