Smoked salmon soufflé with dill (from RimJournal: art and adobe brick, Mexico, the American Southwest, poetry, fiction and food)

Ingredients

• 4 tablespoons (48 g) butter or margarine
• 1/2 cup (110 g) finely chopped onion
• 4 tablespoons (48 g) flour
• 1 cup (240 ml) milk
• 1/2 teaspoon (2 g) salt (optional, smoked salmon is salty)
• dash of cayenne pepper or more to taste
• 1/2 lb. (1/4 kg) grated cheese - Mozzarella or Swiss
• 6 egg whites
• 6 egg yolks
• 1 1/2 teaspoon (7-8 ml) lemon juice (optional)
• 2 cups (450 g) flaked, smoked salmon or the equivalent of canned salmon
• 1/2 to 3/4 cup (110-170 g) finely chopped fresh dill or substitute 3 tablespoons (36 g) dry