Lemon Blueberry Dutch Baby

Dutch Baby Batter
0 Place an 8.5" cast iron pan on the middle rack in the oven. Preheat the oven to 425 F.
2 In a medium bowl, add in the sugar and lemon zest. Rub the zest into the sugar with your fingers. Then add in the eggs, vanilla, and salt and whisk until smooth.
3 Pour in the milk and whisk again.Lastly whisk in the flour. Continue whisking until completely smooth.
4 Cover the bowl and let the batter rest at room temperature for 10 minutes. Then pour the batter through a fine mesh sieve and whisk again.
5 Once the oven has reached 425 F, whisk the batter once more.
Bake
7 Take the pan out and add in a tablespoon of butter. It should melt immediately. Swirl it around the pan into an even layer.
8 Quickly but gently pour the batter into the center of the pan, try not to swirl the butter into it. Sprinkle the batter with fresh blueberries - try to keep a 1-2" border around the edge with no blueberries.
9 Place the pan quickly back into the oven and bake for 20 minutes.
10 If you want to serve with whipped cream, I recommend making it now! Whisk the sugar, vanilla, and salt into them mascarpone, then add in the heavy cream. Whip by hand until smooth with softly whipped peaks.
11 Once baked, it should be puffy and golden brown, remove the pan from the oven and place on a heat safe surface.
12 Squeeze the juice of half a lemon over the top and then dust it with powdered sugar. Optionally serve with spoonfuls of whipped cream.