Heat the oven to 200°C, 180°C, Fan, Gas Mark 6.
Blitz the tomato, onion, carrot and celery together with the garlic, paprika and oregano. Season. Bring to the boil in a pan and simmer for a couple of minutes while you make the white sauce. Melt the butter in a pan and whisk in the flour. Season and gradually whisk in the milk on a gentle heat. Add the bay leaf and nutmeg and cook for a few minutes until thickened.
Blanch the potato slices in boiling water for two to three minutes. Drain and set aside.
Line the bottom of a lasagne dish with a layer of potato followed by half the pork and half the tomato sauce. Top with some white sauce and repeat with another layer. Finish with the potato and white sauce and a good grating of Parmesan.
Bake in the oven for 30 minutes until golden on top.
Serve with buttered shredded savoy cabbage.
3 large red potatoes (about 550g), finely sliced, lengthways,
500g leftover cooked roast pork shoulder, shredded,
1 x 400g can chopped tomatoes,
1 red onion, peeled and chopped,
1 small carrot, peeled and chopped,
1 celery stick, chopped,
1 teaspoon garlic paste,
2 teaspoons smoked paprika,
2 teaspoons dried oregano,
50g plain flour,
300ml skimmed milk,
1 fresh bay leaf,
A grinding of nutmeg,
Freshly grated Parmesan cheese, to garnish