Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch cake pan.
Combine milk, sugar, cornmeal, eggs, butter, all-purpose flour, and baking powder in a blender; mix until very smooth, about 5 minutes. Pour into the prepared cake pan.
Bake in the preheated oven until a toothpick inserted into the cake comes out clean, about 45 minutes. Let cool before cutting and serving.