Cut spring onions and kohlrabi and sauté it in mixture of olive oil and butter. When it gets soft add celery, garlic, salt, pepper and water (1 liter+) and cook 20-30 minutes on easy fire. When the vegetable is soft take blender or stick blender to make creamy mixture. Add semolina into soup. In the meantime cut pancetta into very thin pieces and fry them until crunchy. Put the pancetta onto a paper towel to soak fat. Cook blended soup for 10-15 minutes more. Before serving add heavy cream and parsley. Serve with croutons and pancetta.