Heat oven to 375 degrees F. Liberally grease a large cast iron skillet or 12-inch fluted flan dish.
In a large bowl, beat the eggs and milk together, then gradually stir in the flour, cinnamon, 3/4 cup of the confectioners' sugar and the salt. Beat until smooth.
Gently fold in the blueberries.
Generously butter a large, heavy skillet or 12-inch fluted flan dish.
Bake until golden brown and set, about 45 minutes.
Let cool and sprinkle with the remaining 1/4 cup confectioners' sugar to serve.