Spray a jelly roll pan (I use an 11x17 inch stoneware pan) with no stick cooking spray. Preheat oven to 350 degrees F.

Place the butter in a large saucepan, turn on low heat. As butter starts to melt, whisk in the oil, cocoa, and water. Bring to a boil, over a medium heat, stirring constantly.

Remove from the heat. Using a hand mixer, beat in the sugar and flour. Whisk together the buttermilk, soda, eggs, and vanilla. Beat into batter mixture, adding small amounts at a time. Spread batter into prepared pan.

Bake about 20 minutes, until toothpick inserted into center, comes out clean.

While cake is baking, prepare the icing, the last few minutes.

Place butter in a large saucepan, over medium heat, allow it to start melting. Whisk in the milk, cocoa, and vanilla. Bring to a boil, stirring constantly. Remove from the heat.

Beat in confectioner sugar, gradually. Stir in the nuts. Icing should be thin enough to spread over hot cake. If it seems too thin, add a little more confectioner sugar. If too thick, add small amounts of milk.

Spread icing over the hot cake when it is removed from the oven. Allow to cool at room temperature until icing is hardened and cake is cool.

Cut into 36 squares. Place on serving platter.