Fill the kettle and boil it. Slice a small cross into the bottom of each tomato. Pop them in a heatproof bowl. Pour in enough hot water to cover the tomatoes. Put to one side for 15 mins to loosen the skins. Fill the kettle and boil it again.
Trim the leek. Slice a cross into the top of it. Open it out and rinse out any grit from the layers. Finely slice the leek. Rinse and trim the fennel bulb, saving any frondy bits for garnishing. Finely chop the fennel. Rinse and finely slice the celery.
Warm 1 tsp olive oil in a medium pan. Add the leek, fennel and celery. Season. Cover with a sheet of greaseproof paper. Pop on the lid. Keep the heat very low and sweat the veg for 10 mins till they are soft. Stir now and then to stop them sticking.
While the veg sweat, finely pare or grate the zest from the orange. Juice it. Peel and grate or crush the garlic clove. Rinse the parsley. Pat dry. Finely chop the stalks and leaves, but keep them separate.
Add the garlic, orange zest, parsley stalks and bay leaf to the veg. Cook and stir for 2 mins till the pan smells aromatic.
Fill a measuring jug with 800ml hot water from the kettle. Add the saffron to the hot water. Stir to mix. Add to the pan with the orange juice. Turn the heat up a little to start the water boiling.
Drain the tomatoes. Slip the skins off them. Roughly chop the tomato flesh and seeds. Add to the pan with the fish pie mix. Cover. Gently simmer for 3-5 mins till the fish pie mix is cooked but not broken up.
Taste the stew. Add more salt and pepper if you think it needs it. Ladle into warm bowls. Top with the chopped parsley and any fennel fronds you’ve saved in step 2.