1. To prepare salmon, rinse with cold water.
2. Pat dry with paper towels, and set aside.
3. Combine lemon juice, white wine, olive oil, capers and ¼ teaspoon mustard.
4. Seasoni to taste with salt.
5. Pour over salmon and marinate 30 minutes, turning once.
6. Reserve marinade.
7. Blanchi lettuce leaves in boiling water 5 seconds.
8. Drain well.
9. Arrange 2 leaves with stem ends overlapping at center.
10. Spoon about 2 teaspoons marinade over lettuce.
11. Place 1 salmon fillet on lettuce.
12. Top with 1 or 2 more teaspoons marinade, including some of capers.
13. Roll fillet up. Place 2 leaves on top and tuck edges under fish.
14. Bring up bottom leaf edges.
15. Tie package-style with string.
16. Repeat with remaining lettuce, marinade and fillets to make 4 packages in all. Set aside.
17. To make sauce, blend butter and flour in top of double boiler until smooth.
18. Add vinegar, boiling water, bouillon cube half, ¼ cup mustard, sugar and egg. Cook and stir over hot water until sauce thickens, about 10 minutes.
19. Keep warm.
20. Place salmon bundles on well-greased grill 4 to 5 inches from hot coals and cook 5 to 6 minutes.
21. Turn and cook an additional 5 to 6 minutes.
22. Remove string and serve with mustard sauce.