Sprinkle the flour onto a plate and dredge the lambs’ liver in the flour.
Heat a frying pan until hot, add the butter, oil, lambs’ liver and sweetbreads and fry for 2-3 minutes on each side, or until the lambs’ liver is golden-brown.
Remove the lambs’ liver and set aside to rest, then cook the sweetbreads for a further 2-3 minutes, or until golden-brown and crisp.
Meanwhile, heat the vinegar and sugar in a saucepan until boiling, then add the crushed mustard seeds.
Slice off the white part of the spring onions, add to the saucepan and poach gently for 2-3 minutes, or until just tender. Remove the pan from the heat.
Slice the remaining green part to the onion finely and set aside.
Cook the Jersey Royals in a pan of boiling, salted water for 5-7 minutes, or until just tender, then drain.
Return the Jersey Royals to the saucepan with a little butter, salt, freshly ground black pepper and the mint, and stir until well combined.
Blanch the samphire in a pan of salted boiling water for 1-2 minutes, or until hot through. Drain.
To serve, remove the poached spring onion from the saucepan and add to the samphire, then stir in a little of the poaching liquid.
Arrange the samphire on serving plates with the lambs’ liver and sweetbreads. Stir the dill and sliced spring onion into the remaining poaching liquid and spoon over the plates. Serve the Jersey Royals alongside.