Fill a large Dutch oven half full of water; bring to a boil. Place bratwurst in boiling water; cover and remove from heat. Let stand 5 minutes. Drain well, and pat dry.
Melt butter in a heavy skillet over low heat; add bratwurst, and cook, turning frequently, until browned. Add 1/2 cup water; simmer, uncovered, 15 minutes. Slice bratwurst into 1/4-inch pieces, and remove to a warm serving platter. Set skillet aside with pan drippings.
Combine sour cream, flour, and salt, stirring well. Add sour cream mixture to reserved pan drippings; stir until smooth. Cook over low heat, stirring constantly, 5 minutes, or until mixture is slightly thickened. Add bratwurst slices to sour cream sauce; cook over low heat until thoroughly heated. Serve immediately.