For the streusel:

1. In a small bowl, combine all streusel ingredients. Using a fork or your fingers, mash or pinch together until you have a crumbly mixture that sticks together when you pinch it.

For the muffins:

1. Preheat oven to 400 degrees F.
2. Line 12 cup muffin tin with liners.
3. In a large bowl, mix together flour, cocoa, espresso powder, baking powder, baking soda, and salt. set aside.
4. In a separate medium bowl, mix together eggs, brown sugar, milk, vanilla, vinegar, and olive oil until well combined. I prefer a whisk for this.
5. Next, pour wet ingredients into dry and fold a few times with a rubber spatula or wooden spoon (not a whisk!).
6. Add chocolate chunks and continue folding gently. making sure to get the bottom of the bowl, until you have a mostly mixed, but very lumpy batter.
7. Divide batter between 12 lined muffin cups, filling right up to the top but not over. Divide streusel evenly between muffins, pressing down just slightly so it sticks to the batter.
8. Let pan sit at room temperature for 20 minutes before baking.
9. Bake muffins for 15-18 minutes until just set and no wet batter remains in center. Make sure if you check with a toothpick that you are not confusing the chocolate chunks for wet batter.