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 eggs, milk, vegetable oil, and vanilla extract. Whisk until smooth. Evenly divide cupcake batter between the lined muffin pan and bake for 18-20 minutes. Let cool completely.
For the buttercream frosting, beat softened butter with powdered sugar, milk, and vanilla extract until creamy and smooth. Pipe or spread frosting onto the cooled cupcakes.