Preheat oven to 350° F. Spray a GoodCook Smash Cake Pan with nonstick spray.
In a bowl, combine eggs and sugar and whisk until combined. Add in melted butter and vanilla and stir until incorporated. Add flour, baking powder, and salt, and mix until combined. Stir in milk until incorporated. Pour into prepared pan and cook for 23-25 minutes, or until a toothpick inserted into middle comes out clean. Let cool for 10 minutes in pan, then turn out onto a wire rack to finish cooling.
For the frosting, in a large bowl, blend the butter on medium speed until creamy. Add powdered sugar a little at a time, beating on low, until fully incorporated. Add salt and vanilla and cream and beat on medium speed until light and fluffy, about 3-5 minutes. If the frosting is a little thick, add additional cream until you reach the desired consistency. If too thin, add a little more powdered sugar until reaching desired consistency. If adding food coloring to your frosting, fold in with a spatula until fully incorporated with a consistent color. Frost cooled cake.