Slice butter into pieces and add to a 9x13 inch baking dish.
Place the pan in the oven while it preheats, to allow the butter
to melt. Once melted, remove the pan from the oven.
Add blueberries, sugar and zest to a bowl and stir to combine.
In a separate bowl mix together the batter ingredients: flour,
sugar, baking powder, and salt. Stir in the milk, just until
combined.
Pour blueberries over melted butter in a pan. Drizzle batter
over the top. Sprinkle it with a little bit of cinnamon.
Bake at 350°F (175°C) for about 35-40 minutes, or until lightly
golden on top.
Serve warm, with a scoop of ice cream, if desired!