For batter, combine the eggs, water, flour and salt in a blender. Cover and process until smooth; let stand for 15 minutes.
Meanwhile, in a small saucepan, saute onion in butter until tender. Stir in flour until blended. Gradually stir in milk. Bring to a boil over medium heat, stirring constantly; cook and stir for 2 minutes or until slightly thickened. Reduce heat to low. Stir in 1/2 cup cheese, mustard, Worcestershire sauce, pepper and salt until cheese is melted. Stir in broccoli. Cover; keep warm.
Heat a lightly greased 8-in. nonstick skillet; pour 2 tablespoons batter into the center of skillet. Lift and tilt pan to evenly coat bottom. Cook until top appears dry; turn and cook 15-20 seconds longer. Remove to a wire rack. Repeat with remaining batter, greasing skillet as needed.
Spoon about 1/2 cup filling down the center of each crepe; roll up. Place seam side down in an ungreased 11-in. x 7-in. baking dish. Sprinkle with remaining cheese. Bake, uncovered, at 350° for 5-7 minutes or until cheese is melted.