For the cake:
1 1/2 cups all-purpose flour
1 cup sugar
1/4 cup unsweetened cocoa powder
1/2 teaspoon salt
1 teaspoon baking soda
1 teaspoon vanilla extract
1 teaspoon white vinegar
1/3 cup vegetable oil
1 cup water
For the frosting:
2 Tablespoons butter
1/4 cup unsweetened cocoa powder
1 cup powdered sugar
1 Tablespoon milk (or cream)
1/4 teaspoon vanilla extract
Combine flour, sugar, cocoa powder, salt and baking soda in a large mixing bowl.
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.
Pour batter into a greased 8×8 square pan.
Bake in a preheated 350 degree oven for 30-35 minutes, until toothpick inserted in center comes out clean.
Let cake cool completely before frosting.
How To Make Frosting
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.
Transfer chocolate mixture to a medium size mixing bowl. With mixer on low speed, add in powdered sugar, milk and vanilla.
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.