Preheat oven to 180ºC. Slice the mushrooms in half, or dice if you prefer them finer. In a heavy-based casserole pot, heat 2 tbsp. oil over a low heat. Add the celery, onion, garlic, herbs and 1 tsp salt and sauté for 10 minutes until softened. Increase heat, add the mushrooms and sauté until golden. Remove from pot and set aside.