Make sure ingredients are at room temperature.
Wipe out your cast iron skillet with a cloth or paper towel and place it onto the middle oven rack.
Preheat your oven to 425°F (218°C).
Melt 4 tablespoons of butter and transfer 2 tablespoons to a large mixing bowl. (Reserve the remaining 2 tablespoons to coat the cast iron skillet in step 3.)
Add the remaining ingredients to the mixing bowl and beat for 1-2 minutes using an electric hand mixer. (This can also be done in a blender.)
Remove the cast iron skillet from the oven and swirl the remaining 2 tablespoons of butter to coat the bottom and sides of the pan.
Pour the batter into the pan and bake for 15-18 minutes. (Up to 20 minutes for a 9" skillet.)
Top the dutch baby with a squeeze of lemon juice, berries, powdered sugar, and maple syrup.
Serve while hot.
