In a small bowl, combine 2⁄3 cup (150 mL) blueberries and syrup.
Place 9”x13” metal baking dish in oven and preheat to 425°F (220°C).
In another bowl, whisk together milk, eggs, vanilla, and zest. Add flour, salt and sugar, and whisk until no lumps remain. Stir in blueberry and syrup mixture.
Remove dish from oven, add butter, coating bottom and sides.
Pour batter in, sprinkle with remaining blueberries and put in oven. Bake 20 to 25 minutes, until puffed and deep golden brown.
Dust with icing sugar.
Serves 4 - 6.