1. Combine flour, sugar, cocoa powder, salt and baking soda in a large mixing bowl.
2. In a separate bowl, combine vanilla, vinegar, oil and water. Add wet ingredients to dry ingredients and mix until completely combined and no lumps remain.
3. Pour batter into a greased 8x8 square pan.
4. Bake in a preheated 350 degree oven for 30-35 minutes, until toothpick inserted in center comes out clean.
5. Let cake cool completely before frosting.
1. Melt butter in a small saucepan (or in the microwave using a microwave safe dish.) Stir in cocoa powder, mixture will form a thick paste.
2. Transfer chocolate mixture to a medium size mixing bowl. With mixer on low speed, add in powdered sugar, milk and vanilla.
3. Once ingredients are incorporated, turn mixer to medium high speed and beat about 5 minutes, until frosting is smooth and creamy. Spread on top of cooled cake.