Preheat oven to 350 degrees F (175 degrees C). Grease a 10×15 inch jellyroll pan. In small saucepan, melt 1 cup margarine; stir in 1/4 cup cocoa then stir in water. Bring to a boil; remove from heat.

In a large bowl, combine flour, brown sugar, baking soda, cinnamon and salt. Beat in cocoa mixture. Stir in 1/3 cup sweetened condensed milk, eggs and vanilla. Pour into prepared pan.

Bake in the preheated oven for 15 to 20 minutes, or until cake springs back when lightly touched.

To make the Frosting: In small sauce pan, melt 1/4 cup butter; stir in 1/4 cup cocoa and 3/4 cup sweetened condensed milk. Stir in confectioners’ sugar and nuts. Spread on warm cake.