Pre-heat your oven to 350 degrees.
In a large mixer bowl, sift together flour, sugar, cocoa powder, baking soda, and salt.
Add vegetable oil and sour cream and mix until blended.
Slowly add in water (to prevent water from flying out of your mixing bowl).
Add white vinegar, vanilla extract, and eggs, and mix until blended well.
Place paper liners in your cupcake tin, and fill each about three quarters of the way full.
Bake for around 20-22 minutes at 350 degrees, or until a toothpick comes out clean when inserted.
While cupcakes are baking, begin making peanut butter frosting by combining the cream cheese and unsalted butter in your mixer. Beat until fluffy.
Add in 5 cups of powdered sugar, one cup at a time.
Add in the peanut butter and mix until it's blended well. Make sure to scrape down the sides of your mixer bowl to ensure everything is combined.
When cupcakes have cooled, frost them.
Tip: I bought a super cheap mini cake decorating kit at Target, in the baking aisle, for under $10. It came with a few bags, a few different tips, and an instruction booklet. This is all I use for decorating my cupcakes. They don't look perfect, but they do look better than using a knife to slather on frosting!