In a medium bowl, whisk very well the milk, eggs, vanilla, lemon zest, flour, baking powder, salt and sugar. Make sure there are no lumps. Set aside to rest for 30 min.
Melt the butter and set aside. Measure 1/4 cup of blueberries and set aside.
Place a 9 by 13 inch baking dish (or similar size) in your oven and preheat to 425° F.
Add the remaining 1/2 cup of blueberries and maple syrup in a small sauce pan. Heat on low until the blueberries are warm. Mash them a bit with a fork. Set the sauce aside.
Remove the baking dish from the oven and quickly pour in the melted butter. Brush butter up the sides of the dish and pour in the batter. Top with reserved blueberries and return to the oven as fast as you can.
Bake for 20-25 minutes, or until set. If after 15 minutes the pancakes are already browned, cover loosely with tin foil. The pancakes with rise very high and be very puffy.
When taken out of the oven, they will deflate. Top with lemon zest and/or icing sugar if desired. Serve the cut portions on plates and spoon the blueberry sauce on top.