Preheat oven to 425 degrees. Line 2 12-cup muffin tins with parchment or paper liners.
In a large bowl, beat the oil and sugar until combined, about 1-2 minutes. Whip in the eggs, one at a time, until fully incorporated, then the vanilla and Greek yogurt. With the mixer running, stream in the buttermilk until the batter is smooth.
Scrape down the sides of the bowl as needed with a spatula. Add the flour, cocoa powder, baking powder, instant espresso (if using), and salt. Mix until just combined. Fold in the chocolate chips with a spatula. Do not overmix that shit.
Cover the bowl with plastic and let the batter sit at least 15 minutes. Overnight is best, but most of us don't got time for that.
Remove the plastic from the bowl. Scoop the batter into the lined muffin tins. Don't be afraid to fill them all the way to the top! You will get anywhere from 16-18 muffins depending on how much you fill them.
Sprinkle each muffin with a few more chocolate chips. Bake for 5 minutes at 425, then reduce the oven temperature to 350 without opening the door. Bake 12-16 minutes longer until the centers are set and an inserted toothpick emerges with just a few moist crumbs.
Let cool 5 minutes in the pans, then transfer to a wire rack. Eat one or two warm (mmmHMMM), or let cool completely and store in a covered container for up to 5 days at room temperature, a week in the fridge, or 2 months in the freezer.