Preheat oven to 350 degrees Fahrenheit.

Sift flour, 1 cup sugar, 1/3 cup cocoa powder, baking soda and salt into an 8" square pan.

Make three 2" holes in flour mixture with fork.

Pour warm water and 1 teaspoon vanilla into 1 hole.

Pour vegetable oil into the second hole.

Pour vinegar into the third hole.

Stir through batter until well mixed, 1-2 minutes.

Bake until toothpick inserted in center comes out clean, about 30 minutes.

Cool cake completely in pan.

For the icing, combine remaining 1/2 cup sugar, butter, milk, and 2 tablespoons cocoa powder in small saucepan over medium heat and bring to boil.

Reduce heat and simmer 1 minute.

Remove from heat and stir until cool, about 5 minutes.

Add remaining 2 teaspoons vanilla and mix well.

Spread icing over cake in pan.

Let cool until set.