Preheat your oven to 350F (175C) and line a muffin tin with cupcake liners.
In a large bowl, whisk together the flour, cocoa powder, baking soda, sugar, and salt.
Make a well in the center of the bowl and add the vinegar, vanilla extract, oil, and water. Use a large wooden spoon to stir the ingredients together until they are well-combined.
Fill each cupcake liner to the 3/4 mark and bake for 15-20 minutes.
When the cupcakes are baking, make your frosting: Use a hand (or stand) mixer to cream together the peanut butter and chilled coconut oil. When fully combined, add the remainder of the ingredients and beat for another 2 minutes on high. Set this in the fridge until you're ready to use it.
Allow cupcakes to cool and apply a THICK layer of frosting to them! Leave them in the refrigerator until ready to serve.