Heat the oil in a frying pan, add the onions and sauté on a gentle heat until soft. Stir in the Henderson’s Relish, thyme and sugar. Cook over a low heat until the mixture has caramelised, becoming sweet and sticky, then remove from the heat and leave to cool slightly.
FOR THE PLOUGHMAN’S RAREBIT
Lightly toast chunky slices of sourdough bread or crumpets. In a bowl, combine the chopped ham and all the cheeses with the beaten egg, mustard, and black pepper. Spread a layer of the Hendo’s onion marmalade on the toast or crumpets, then top with a layer of the ham and cheese mixture, making sure it reaches right to the edges. Place the rarebit under a medium grill to melt, then turn up the heat to glaze the top until golden and bubbling.