Melt butter in a saucepan.

Add brown sugar and cream. Cook over medium-low heat for about 2 minutes until the sugar is dissolved.

Remove from heat and add vanilla.

Transfer to a large bowl.

Using a handheld electric mixer, beat in confectioners’ sugar until smooth. If frosting is too thick, add 1 tablespoon heavy cream at a time until consistency is right.

Spread onto cooled cake. Top with walnuts nuts if desired.