Grease 4 souffle dishes (1/2 cup capacity), sprinkle with breadcrumbs.
Melt butter in small saucepan, add finely chopped onion. Stir over low heat for 2 minutes . Cook until onion is soft, it doesn't have to become brown.
Stir in flour and stir over medium heat for a minute. Remove from heat, gradually stir in milk, bring back to heat and stir over high heat until mixture boils and thickens and reaches a thick sauce like consistency.
Transfer to large bowl, stir in tomato paste and basil leaves. Cover the dish and let it stand for 5 minutes.
Beat egg whites in a small bowl until soft peaks from. Add egg yolks to the onion and milk mixture, and mix well. Fold the egg whites into the mixture in 2 batches.
Pour the mixture evenly into the prepared dishes. Sprinkle the grated cheese on top. Bake in the preheated oven for 20- 25 minutes or until lightly browned.