First, gently pan-fry the onion over a low heat in a splash of olive oil, along with the sugar and some salt and pepper, for at least 20 minutes. Once caramelised and dark brown, remove from the heat and set to one side.
To make the Welsh rarebit, preheat your oven to 190ºC/gas mark 5.,Grab a bowl and finely grate the Cheddar using the finest grater you have. Add a splash of single or double cream and mix with a fork to create a paste (about the consistency of mashed potato).
Cut the baguette at an angle into 1cm-thick slices and place on a wire rack. Top each piece with a dollop of the cheese mixture and add a splash of Worcestershire sauce to each one.
Place each slice of bread with cheese mixture on into the oven, and cook it for about 10 minutes, or until the cheese is bubbling and the bread is toasted.
Assemble the salad leaves and the rarebit pieces on a large platter, then spoon a teaspoon of the caramelised onions onto each of the cheese toasts. Sprinkle over some pine nuts, drizzle with olive oil and serve.