Preheat your oven to 375°F and line your muffin tin with 4 cupcake liners.
In a small bowl, whisk together flour, baking powder, espresso powder, and salt. Set aside.
In a medium bowl, combine sugar and oil, and whisk until well-combined. Add egg white, sour cream, and vanilla. Whisk until smooth. Stir in flour mixture until just combined and then fold in chocolate chips.
Divide mixture between your prepared muffin tins. Bake for 17 to 21 minutes, until a toothpick inserted into the center of the muffins comes out with only a few dry crumbs and when gently pressed, the muffin top springs back.
Cool for 5 minutes before transferring to a cooling rack to finish cooling.