Preheat the oven to 400°F (200°C).
In a blender or with a hand mixer, combine the eggs, whole milk, all-purpose flour, granulated sugar, lemon zest, and salt until the batter is smooth and slightly frothy.
Place a 12-inch cast iron skillet over high heat and add the unsalted butter; melt until it foams and just begins to brown.
Pour the batter into the hot skillet, then evenly scatter the blueberries and halved raspberries over the batter.
Transfer the skillet to the preheated oven and bake until the pancake is puffed and set in the center, about 20 minutes.
Remove from the oven, slice, and serve warm topped with powdered sugar, syrup, and/or freshly whipped cream as desired.