Preheat oven to 350 degrees F. Place rack in lower third of oven. Spray two 9" round cake pans with a good coat of non-stick cooking spray.

Sift together flour, both cocoa powders, baking powder, baking soda, and salt three times. Yes, THREE times to fully incorporate everything together; set aside.

Whisk together yogurt and 1/4 cup lukewarm water; set aside.

Whisk together eggs and vanilla; set aside.

In a large mixing bowl, beat 2 sticks of butter on medium speed until light and fluffy. Turn mixer to low and stream in sugar. Beat until combined and smooth, about 2 minutes on medium-high speed. Turn mixer back to lower and stream in egg mixture. Mix until combined; scrape the sides of the bowl with a spatula, as needed.

With the mixer on low speed, add 1/3 of the cocoa mixture to the batter, and beat until just combined. Add 1/2 of the yogurt mixture, and beat until just combine. Repeat with 1/3 cocoa mixture, remaining half of yogurt mixture, and last 1/3 of cocoa mixture; beat until just combined after each addition. Scrape the bowl with a spatula as needed.

Divide the batter between the two prepared pans. Slam the pans on the counter top a couple times to remove bubbles and even batter.

Bake 25 to 30 minutes or until a toothpick inserted in the center comes out clean. Remove cakes to a wire rack to cool completely. Remove from pans.

Combine all ingredients in a medium bowl until smooth. Carefully place one half on the cooled cake on a serving plate {bottom side down}. Top the cake with all the peanut butter frosting and smooth over the top of the cake only, not down the sides. Add the second cake layer on top of the frosting {bottom side up, to give your cake a smooth top} and press down gently.

Place a medium sized glass bowl over a pot of simmering water. The bowl should rest above the water {not touching the water}. Add dark chocolate chips to the bowl. Stir chocolate occasionally until completely melted and smooth.

Remove bowl from heat and stir in sour cream until ingredients are combined and smooth. Frost cake until completely covered.