Line a 6-count jumbo muffin pan with paper liners and set aside.
In a large mixing bowl, sift together all-purpose flour, sugar, cocoa powder, cornstarch, baking powder, baking soda,
espresso powder and salt.
In a medium mixing bowl, whisk together olive oil, eggs, sour cream, buttermilk and vanilla until well combined.
Pour wet ingredients into the dry ingredients and mix until there are very few flour steaks left. Do not overmix.
Then, gently fold in the chocolate chunks or chips. Cover with a tea towel and allow the batter to rest on the counter for at least 45 minutes.
With 15 minutes left of resting, set a rack in the center of the oven and set it to 425ºF.
Evenly divide the batter in each muffin cavity. It should be filled nearly to the brim. Top with extra chocolate chunks.
Bake muffins at 425ºF (218ºC) for 6 minutes and then lower the temperature to 350ºF (without opening the oven door) and continue baking for 20 to 24 minutes. They are ready when a toothpick inserted in the center comes out with very few moist crumbs. Keep muffins in the pan for 5 minutes and then transfer to a wire rack to cool.
Meanwhile, as the muffins are cooling, make the chocolate ganache. Finely chop your chocolate and transfer to a heatproof bowl. Heat the cream in a small saucepan just until simmering. Then pour hot cream over chocolate and let stand, untouched for 4 to 5 minutes. Gently and slowly stir until combined. Transfer ganache to a piping bag, ziploc bag or squeeze bottle
With a knife or large decorating tip, scoop out a deep hole in the center of each muffin. Then, generously fill with chocolate ganache. Serve and enjoy.
NOTES: Storee muffins in an airtight container at room temperature for up to 2 days or in the fridge for up to 1 week.