Melt the butter over low heat in a 10-inch cast iron skillet.
Bring one cup of water to a simmer in a small saucepan.
In a medium size bowl add flour, 1 cup of the sugar, baking powder, baking soda, and salt and stir until well blended.
Swirl the melted butter around the cast iron pan so that the butter coats about halfway up the sides of the pan.
Pour in the butter from the skillet into the flour mixture and add the buttermilk and 1/2 cup water and stir until well combined. (not the boiling water, tap water)
Add the batter to the skillet and distribute blueberries over the top. Tip: The blueberries will sink in the batter so if you want some blueberries on the top of the cobbler, reserve a few and add after 25 minutes of baking.
Sprinkle the remaining 1 cup of sugar evenly over the top of the blueberries.
Pour the boiling water over the sugar.
Bake in a 350° oven for 45 – 55 minutes, until cobbler is set and top is golden brown.
While cobbler is baking, make the Hazelnut Cream Sauce.
In a small bowl combine the heavy cream, sweetened condensed milk, and Frangelico or liqueur of your choice.
Serve the cobbler while it is still warm and liberally drizzle the hazelnut cream sauce over the top.