Combine sugar, flour and salt. Gradually stir in water and vinegar. Cook, stir until thickened and bubbly. Reduce heat, cook and stir 2 minutes longer. Remove from heat.
Stir small amount of dressing into eggs. Return all to pan, stirring constantly. Bring to a gentle boil, cook, and stir 2 minutes longer.
Serve over spinach and sliced mushrooms and sprinkle with bacon and croutons.
May be kept in a slow cooker on low. Makes 6 1/2 cups. Refrigerate any leftovers.
Notes
This recipe makes a lot of dressing, but it can be halved or quartered if desired.