Preheat the oven to 180C.
Arrange the tomatoes in a baking tin, cut side up. Drizzle over 1 tablespoon of olive oil, then sprinkle ½ tablespoon dried oregano / marjoram and seasoning on top. Lightly massage, then place in oven and roast for 45 minutes – 1 hour until softened and lightly charred.
Heat remaining oil in a large pan over medium heat. Add garlic and gently cook for 2 minutes, stirring occasionally. Add diced onion, celery and marjoram/oregano and cook for 10 minutes more. Add tomato puree, cook for 1 minute.
Add the roasted tomatoes and stock and bring to the boil.
Reduce heat and simmer for 20-30 minutes until slightly reduced, then add basil and blitz with a hand blender until smooth. Season lightly to taste.
Use as desired.