When I was young, I despised tomato soup. I always thought it tasted of tomato sauce, which is strange because I liked tomato sauce (ketchup) on everything. But now, I appreciate its subtle acidity and its gentle sweetness. And when served with a rich, oozy, toasted cheese sandwich, it’s simply perfection.     I call these my ultimate toasted cheese because they are by far the best I’ve tasted. They are simple with only one secret ingredients, a slow-braised onion purée flavoured with butter and white pepper. This purée mimics the texture of the melted cheese and infuses the sandwich with sweet, buttery, peppery flavour which is just to-die-for. I’m not quite…