Heat oven to 375°F. Butter bottom of 1 1/2-quart soufflé dish. Tie double-thickness of aluminum foil collar around dish, extending 2 inches above top.
In medium saucepan, melt 3 tablespoons butter over medium heat. Add onions; cook 2 to 3 minutes or until slightly softened. Stir in flour and pepper. Cook, stirring constantly, 1 minute longer. Stir in milk; cook, stirring constantly, 4 to 5 minutes more or until mixture thickens and boils. Reduce heat to low.
In small bowl, beat egg yolks lightly. Stir in small amount of hot white sauce, mixing well. Add yolks and cheese to thickened sauce; cook, stirring constantly, 2 to 3 minutes or until thickened. Remove from heat.
In food processor bowl, process SPAM® Classic and broccoli. Or, finely chop by hand. Stir into white sauce.
In clean bowl, combine egg whites, salt and cream of tartar. Beat with electric mixture until stiff (but not dry) peaks form. Gently fold into SPAM® mixture. Spoon mixture into soufflé dish. Bake 35 to 40 minutes or until lightly browned and set. Serve immediately.