In a large frying pan, add all sauce ingredients and heat until boiling. If using frozen berries, toss the thawed berries with cornstarch before placing them in the pan. Once the sauce is boiling, reduce heat and simmer for 5 minutes.
While sauce is simmering, combine flour(s), baking powder and salt. Cut in butter until the mixture looks like crumbs. Add 1 tbsp maple syrup to the bottom of a measuring cup and then fill to ¾ cup with milk. Add milk and syrup to flour mixture and stir until just combined.
Drop dough by heaping spoon-fulls onto simmering blueberry sauce. You should have about ten dumplings.
Cover the pan with a lid, and cook for 15 minutes.