Get out and measure your ingredients.
Using your small mirowave safe bowl combine melted butter and cocoa until resembles a sort of paste. Grb your pastry brush and make sure to coat every inch of the inside of your baking pan. If butter begins to harden microwave bowl for 15 seconds or butter softens.
Preheat your oven to 350 degrees and adjust your oven rack to lower-middle position.
Using your heat resistant bowl and add cocoa, chocolate, and espresso powder together.
Carefully pour boiling water all over top of the mixture.
Using your whisk, stir until blended and smooth.
Allow mixture to cool to room temperature and whisk in sour cream.
Keep whisking until blended.
In a seperate, large bowl combine flour, baking soda and salt.
Whisk until blended.
Using your handheld or stand mixer beat butter, sugar, and vanilla together on medium high speed.
Beat until fluffy, around 3 minutes.
Reduce speed to medium and gradually add eggs, one at a time, blending after each for about a minute, scraping down bowl sides as necessary until totally blended.
Batter might look like it is seperating. Reduce mixer speed to medium-low and add about half of the flour mixture.
Add about half of chocolate/sour cream mixture too.
Blend until just incorporated. Less than 30 seconds. Scrape down sides of bowl as necessary, and add remaining flour mixture, followed by remaining chocolate/sour cream mixture. Blend until just combined. Do not over mix.