Preheat oven to 350 F. Line a 12 cup muffin pan with cupcake liners. In a large bowl, whisk together flour, sugar, salt, and baking powder.
Add in milk, vegetable oil, eggs, and vanilla extract, whisk until smooth. Evenly divide cupcake batter between the prepared cupcake liners. Bake for 15-18 minutes. Let cool completly.
In a large bowl, beat softened butter with softened butter, powdered sugar, milk, and vanilla extract until smooth. Pipe frosting onto cooled cupcakes.