1) Preheat oven to 400°.
2) Lightly spoon the flour into dry measuring cups and level with a knife. Combine the flour and the next brown sugar, cocoa, baking powder, baking soda, and salt in a large bowl. Make a well in the center of the dry mixture and set it aside.
3) Place the black beans, water, oil, vinegar, unsweetened applesauce, dates (don't forget to remove the pits first!), vanilla and egg in a blender. Blend well until completely smooth. Combine the wet mixture with the flour mixture and stir just until moist. Gently fold in 2/3 cup of the mini chocolate chips.
4) Spray enough muffin tins with cooking spray to make 18 muffins. Divide the batter evenly among the muffin cups. To make Reese's-style muffins, swirl about a teaspoon or so of peanut butter into the batter (optional). Sprinkle the remaining mini chocolate chips evenly over the batter. Bake at 400° F for 10 minutes or until a wooden pick inserted in the center comes out clean. Be careful not to overbake. Cool the muffins in the tins for 5 minutes on a wire rack.