Preheat your oven to 350°F (175°C).
Line your cupcake pan with cupcake liners.
In a large mixing bowl, combine the vanilla cake mix, sugar, flour, water, eggs, vanilla extract, sour cream, and softened butter. Beat on medium speed for about 2 minutes until smooth.
Fill each cupcake liner about two-thirds full with the batter.
Bake for 18-20 minutes, or until a toothpick inserted comes out clean.
Cool the cupcakes in the pan for about 5 minutes, then transfer to a cooling rack.
For frosting, beat together the softened butter, powdered sugar, 2 tsp vanilla extract, whipping cream, and a pinch of salt until light and fluffy.
Once the cupcakes are cool, frost each cupcake generously.