• Preheat your oven to 350 degrees F.
• Line a 8"x8" square pan with parchment paper. Grease the paper. Set aside.
• In a medium mixing bowl, whisk together the dry ingredients (flour, sugar, soda, salt and cocoa).
• In another mixing bowl, whisk together the wet ingredients (oil, water, vanilla and vinegar).
• Add dry ingredients to wet ingredients and whisk together until smooth.
• Pour the batter into prepared pan.
• 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!)
• Cool in pan for 2 minutes. Transfer onto a cooling rack to cool completely before frosting.

to make the frosting:

• Melt butter in a medium saucepan. Take off the heat.
• Whisk in cocoa and sour cream/Greek yogurt.
• Place back on the burner and cook just until it starts to bubble.
• 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.
• Transfer the mixture into a bowl.
• Sift the sugar over the bowl and whisk it in.
• Add vanilla and mix well.
• Let the frosting cool for 10 minutes.
• Spread over the cake.
• It will set more as it cools.