Preheat the oven to 425 degrees and place the cast iron pan inside to warm up.
In a medium-side bowl mix the flour, milk, lemon zest, lemon juice, and salt together. Set aside. Leaving some lumps of flour is a good thing. Do not over-mix.
In a separate bowl gently whisk the eggs.
Fold the eggs into the batter until fully incorporated.
Very carefully, remove the cast iron from the oven, place butter in the hot pan and melt.
Pour in the batter.
Sprinkle berries evenly across the batter.
Return to oven and bake for 20 minutes until the sides start to brown and the middle is set. Make sure to turn on your oven light and watch your dutch baby come to life.
Remove from oven and allow to cool for 5 minutes.
Top with your desired toppings such as confectioners sugar, syrup, more fresh berries, or even a jam or berry sauce.