Place a 12" cast iron pan on the middle rack in the oven. Preheat the oven to 425 F.
In a medium bowl, whisk together the eggs, sugar, lemon zest, vanilla, and salt.
Pour in the milk and whisk again.
Lastly whisk in the flour. Continue whisking until completely smooth.
Let the batter rest for 10 minutes. Then whisk again.
Once the oven has reached 425 F, whisk the batter once more.
Take the pan out and add in 2 tablespoons of butter. It should melt immediately.
Once melted, quickly pour the batter into the center of the pan, try not to swirl the butter into it.
Place the pan quickly back into the oven and bake for 25 minutes.
Once baked, it should be puffy and golden brown, remove the pan from the oven and place on a heat safe surface.
Squeeze the juice of half a lemon over the top and then dust it with powdered sugar. Serve immediately with spoonfuls of the whipped berry butter.