Preheat oven to 375º. Beat cream cheese, egg and sugar in a mixing bowl until well blended and creamy. Mix in chocolate chips and set aside.
Add vinegar to milk in a small bowl and set aside until milk has curdled (5 minutes).Meanwhile, in a large bowl, combine mesquite flour, cocoa, baking soda and salt until well mixed. Add milk-and-vinegar mixture along with the oil and vanilla into the mesquite flour and mix well.
Line a muffin tin with paper liners and fill half full with batter. Spoon one tablespoon of cream cheese mixture on top of the mesquite batter. Using a sharp knife, swirl the cream cheese mixture into the batter, creating a marbled effect. Be careful not to over mix. Bake for 35 to 40 minutes. A toothpick inserted into the center of the cake should come out slightly moist.
Reprinted with permission from Eat Mesquite! A Cookbook by Desert Harvesters