In a large mixing bowl, sift together dry ingredients: flour, cocoa powder, baking soda. baking powder, salt and espresso powder. Set aside.
In a separate bowl, use an electric mixer to beat together oil and both sugars.
Add eggs, one at a time, beating after each addition until well incorporated.
Beat in sour cream, vanilla and grated zucchini until combined.
Gradually add dry ingredients to wet, beating on low speed until just combined. Do not overmix.
Add chocolate chips, stirring with a spoon until evenly distributed.
Place batter in the refrigerator to chill while oven preheats.
Preheat oven to 425 degrees. Line a muffin tin with paper liners then set aside.
After oven has finished preheating, remove batter from refrigerator and fill muffin liners all the way to the top. Return remaining batter to the refrigerator until it's time to bake the second batch.
Bake muffins for 5 minutes at 425 degrees then, keeping the oven door closed, reduce oven temperature to 350 degrees and bake an additional 12 to 15 minutes or until a tester inserted into the center of a muffin comes out clean.
Allow muffins to cool in baking pan for 5 minutes then place muffins on a wire rack to cool completely.
After muffin tin has cooled to room temperature, increase the oven temperature to 425 degrees and repeat the baking process for your remaining batter
Cover and store muffins at room temperature up to 3 days or in the refrigerator up to 5 days.