Combine cornmeal, 3 tablespoons flour, and salt in a medium mixing bowl. Add 1 1/2 cups cold water, stirring until well blended
Bring 4 1/2 cups water to a boil in a large Dutch oven; add cornmeal mixture, stirring until well blended. Reduce heat; simmer 10 minutes, stirring frequently. Pour mixture into a lightly greased 15- x 10- x 1-inch jellyroll pan. Cover and refrigerate overnight.
Cut mush into 3- x 2-inch pieces; dredge in remaining flour. Fry in hot oil (375°) in a large skillet, a few pieces at a time, turning occasionally until golden brown on both sides. Drain well on paper towels. Serve warm.