Method:
1. Melt a large knob of butter with a generous glut of extra virgin olive oil. Add the onions, and season well with salt. Leave to caramelise. This could take 30-40 minutes, and will vary dependent on the variety of onion being used. Do not rush this stage, and do not burn the onions.
2. Once the onions are almost there, add the vinegar. Continue to cook down until the onions are sticky and jammy. Leave to cool slightly.
3. Layer the onions on the base of the plate, followed by shavings of the cheese and finally the prosciutto. Best served with good bread.
