Use a blender or hand mixer to combine the eggs, milk, flour, sugar, lemon zest and salt.
Heat a 12-inch cast iron skillet over high heat on the stove. Add the butter and melt. Pour the batter into the skillet, then scatter the berries on top. Put the pan in the oven, and bake until puffed and cooked through, about 20 minutes. Slice and serve, topped with powdered sugar, syrup and/or freshly whipped cream, as desired.