Preheat the oven to 375F and place a rack in the top 1/3 of the oven, at least 6-inches from the heat source. Grease a regular muffin tin or use muffin liners.
In a large bowl, whisk together the butter, granulated sugar, brown sugar, eggs, espresso and vanilla until completely blended together.
In a medium bowl whisk together the flour, cocoa powder, baking soda, baking powder, ground espresso and sea salt. Alternate adding the flour mixture and the buttermilk into the butter mixture in two batches, ending with the buttermilk. Stir until barely combined and you still see streaks of flour. Fold in the chocolate chips, reserving about 3 tablespoons of chocolate chips for the tops of the muffins. Scoop the batter into the muffin liners and fill until just barely ¾ full. Let the muffins sit for 15 minutes before putting in the oven; this helps them get a wee more rise (and is optional).
Coarsely chop the 3 tablespoons of chocolate that you set aside and sprinkle over the tops of the espresso muffins.
Bake for 15 minutes in the top third of the oven or until a toothpick comes out clean. You want the tops to be puffed up. For best results, bake one tin at a time.
Let cool in the muffin tin for about 10ish minutes, then use a butter knife to help get them out to finish cooling on a rack.
*I use a Nespresso espresso pod for this. You could sub in any finely ground coffee or as noted in the comments below, espresso powder.