Preheat oven to 400 degrees F (200 degrees C). Grease a 9x13-inch baking dish.
Beat eggs in a bowl; stir in milk, butter, and vinegar. Stir cornmeal, millet flour, sugar, baking powder, and salt into egg mixture until combined; spread batter into prepared baking dish.
Bake in preheated oven until golden brown, 16 to 20 minutes. Cool on wire rack for 10 minutes.
