Lady Bird Johnson's Mexican Chocolate Cake

1/2 cup (1 stick) margarine
1/2 cup vegetable oil
2 (1 ounce) squares unsweetened chocolate or 4 tablespoons cocoa
1 cup water
2 cups sifted all-purpose flour
1 teaspoon baking soda
2 cups granulated sugar
1/2 cup sour milk (place 1 1/2 teaspoons vinegar
    in 1/2 cup measure, then fill with milk)
2 eggs, beaten
1 teaspoon cinnamon
1 teaspoon vanilla extract

Icing:
1/2 cup (1 stick) margarine
4 tablespoons cocoa
6 tablespoons milk
1 (1 pound) package confectioners' sugar
1 teaspoon vanilla extract
1/2 cup pecans

Heat oven to 350 degrees F. Grease a 12 x 18-inch cake pan.

Combine margarine, oil, chocolate and water in a saucepan. Heat until chocolate is melted.

Combine flour, soda, sugar, milk, eggs, cinnamon and vanilla extract in large bowl, then combine with first mixture. Pour batter into prepared cake pan. Bake 20 to 25 minutes or until cake is done.

Ice cake while still warm.

Icing: Combine margarine, chocolate and milk in a saucepan. Heat until bubbles from around the edge. Remove from heat. Add confectioners' sugar, vanilla extract and pecans. Beat until smooth.