Instructions: Slice the top off the muffin, scoop out the centre and place the cases on a baking tray with the top. Sweat the leeks. Once soft, add the creme fraiche and mustard. Stir and season with salt, pepper and nutmeg.

Crumble in the mackerel and stir again. Heat the muffin cases in the oven with the tomato slices. When they are warm and crisp, fill with the leek and mackerel mixture and top with a slice of tomato.

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