Preheat oven to 180 degrees. Beat the condensed milk and the butter in a large bowl. Add the eggs, one by one. Add the lime zest and the evaporated milk alternately with the flour. Pour batter into a greased and floured cake pan. Bake for 35 minutes or until toothpick inserted in center comes out clean. Invert after 10 minutes and let cool. Level top of cake and pour rompope evenly.
For the frosting, beat both ingredients until well combined. Frost cake and garnish as desired.