Vegetable stock paste

Name: Vegetable stock paste
Prep time: 10 min
Cook time: 30 min
Total time: 40 min
Cuisine: European, British
Ingredients: 200 g celery stalks, trimmed, cut into pieces; 2 carrots, cut into pieces; 1 brown onion, cut into halves; 1 fresh tomato, cut into halves; 1 zucchini, cut into pieces; 2 garlic cloves; 1 dried bay leaf (optional); 1 - 2 sprigs fresh basil, leaves only; 1 - 2 sprigs fresh sage, leaves only; 1 - 2 sprigs fresh rosemary, leaves only; 8 sprigs fresh flat-leaf parsley, leaves only; 150 g rock salt; 1 tbsp olive oil