In a large bowl, combine the cake mix, peanut butter, ½ cup of the melted butter and eggs. Stir until blended. Press ⅔ of the mixture into a 9x13-inch ungreased pan.
In a separate bow. combine the condensed milk, 2 tablespoons of melted butter, vanilla and salt. Stir in the chocolate chips, coconut and nuts. Spread this mixture evenly over the cake mix layer. Crumble the reserved dough over the top.
Bake 25 to 30 minutes, or until golden. Cool for at least a couple of hours, and then cut into squares.
Keep bars stored in a sealed container for up to 3 days. These can be stored in the freezer for up to 3 months.