Boil penne pasta in three to four cups of water. Do not overcook. Drain, refresh in cold water. Drain and keep aside. Wash basil leaves and keep them in cold water to be used for garnishing. Heat olive oil in a pan and add bay leaf and onion and sauté till translucent.
Add celery and leek and stir-fry for a two to three minutes. Add tomatoes and sauté. Add vegetable stock and cook on high heat for ten minutes, stirring occasionally. Reduce heat and simmer for about five minutes. Remove from heat and cool. Puree tomato mixture in a blender. Heat butter in a pan. Add whole wheat flour and cook on medium heat for two to three minutes, stirring continuously.
Add skimmed milk, a little at a time, and stir continuously to avoid lumps. Cook on low heat till you get a thick sauce. Season with salt and white pepper powder. Stir in pureed tomato sauce, capsicum and boiled penne pasta. Heat thoroughly, add mixed dried herbs and serve hot garnished with basil leaves.