1. Preheat your oven to 350 degrees F.
2. Line a 8"x8" square pan with parchment paper. Grease the paper. Set aside.
3. In a medium mixing bowl, whisk together the dry ingredients (flour, sugar, soda, salt and cocoa).
4. In another mixing bowl, whisk together the wet ingredients (oil, water, vanilla and vinegar).
5. Add dry ingredients to wet ingredients and whisk together until smooth.
6. Pour the batter into prepared pan.
7. Bake for 23 to 28 minutes, or until the toothpick inserted into few place in the cake comes out clean. (Out of toothpicks? Use an uncooked spaghetti noodle!)
8. Cool in pan for 2 minutes. Transfer onto a cooling rack to cool completely before frosting.

to make the frosting:

1. Melt butter in a medium saucepan. Take off the heat.
2. Whisk in cocoa and sour cream/Greek yogurt.
3. Place back on the burner and cook just until it starts to bubble.
4. Alternately, you can melt the butter in a microwave safe dish, whisk in the cocoa powder and Greek yogurt and cook for 10 to 15 more seconds, just until it starts to bubble.
5. Transfer the mixture into a bowl.
6. Sift the sugar over the bowl and whisk it in.
7. Add vanilla and mix well.
8. Let the frosting cool for 10 minutes.
9. Spread over the cake.
10. It will set more as it cools.