Preheat oven 350 degrees. Grease and flour a 13x9x2 inch baking pan.
Combine and mix well cake mix, butter, eggs, water, oil and 1/2 can sweetened condensed milk. Pour half of the batter into the prepared baking pan. Bake for 20 to 25 minutes.
In a saucepan over low heat, combine caramels and 1/2 can sweetened condensed milk. Stir mixture, heating until caramels are melted and mixture is smooth. Evenly spread over the baked cake layer. Sprinkle generously with chopped pecans. Cover with remaining cake batter. Bake 25 to 30 minutes longer or until cake springs back when lightly touched. Frost with Turtle Cake Frosting.
Turtle Cake Frosting:
Combine butter, cocoa, and evaporated milk in a small saucepan. Heat, stirring, until butter is melted and mixture is well blended. Remove from heat and add confectioners' sugar and vanilla. Spread over cooled cake.