Heat over to 375. Grease muffin cups or use foil baking cups.
Beat sugar and butter in large bowl until pale and fluffy. Beat in eggs one at a time. Add yogurt, orange juice, baking powder, and baking soda. Mix very well. Batter will be quite liquid!
Sprinkle flour, then chocolate chips, over batter. Fold gently, just enough to blend in flour.
Scoop batter into muffin cups. Bake 15-25 minutes, or until golden brown and springy to the touch. Turn out onto a rack to cool.