Beat cream cheese, butter, eggs, and vanilla until smooth and fluffy. With the mixer on low, add in the box of powdered sugar and beat until creamy and combined. Spread over the first layer.
Bake the butter cake for 40 minutes until golden and puffy.
Make a butter sauce by combining butter, sugar, and evaporated milk. Bring to a simmer and cook bit more, whisking regularly. Remove from heat and whisk in vanilla extract.
Pour butter sauce over butter cake (either warm or after the cake has cooled) and serve.