1. Pre heat oven to 190/gas mark 4. Place the pepper & onion halves (cut side down) along with the plum tomatoes & garlic cloves into a baking tray & drizzle with the olive oil. Bake at the top of your oven for 30 minutes or until the vegetables are roasted & tender.
2. Meanwhile melt down the butter in a large pan over a medium heat and sauté the chopped celery for 4-5 minutes. Not too hot, don't burn the butter.
3. Make up the vegetable stock adding the tomato puree, sun-dried tomato paste & the chilli flakes. Mix well and then add to the sautéed celery. Remove from the heat.
4. When the baked vegetables are ready remove the peel from the onion & garlic cloves roughly chop them & add them to the pan along with the plum tomatoes. Place back on to a low to medium heat & using a hand blender blend until the soup is smooth.
5. Season to taste & gently simmer until the soup is at a comfortable edible temperature. Do not allow the soup to boil.