Preheat oven to 350
In a bowl, combine milk, flour, and melted butter and stir with a whisk until mostly a smooth consistency, and set aside
Add Blueberries, lemon juice, cinnamon, sugar and 3 TBSP of water to the dutch oven and stir well
Cook at medium temperature at a low boil for about 5 minutes until the blueberries start to burst
The mixture will begin to thicken slightly, use a spoon to help smash the remaining blueberries
Make a slurry with the cold water and the arrowroot powder/cornstarch and add to the mixture stirring well
Continue to cook until it comes back to a boil. It will become much thicker (between syrup and jelly consistency) you can remove from heat at this point
Pour the cobbler dough mixture over the top of the thickened blueberries
Bake for 30-35 minutes until a knife inserted into the dough comes out clean
Serving suggestion: serve warm with fresh whipped cream, or vanilla ice cream