Note Cantal, a semi-hard cow's milk cheese from France's Auvergne region, is available from select delicatessens. If it's unavailable, substitute 100gm raclette and 100gm Gruyère. If you can't fit a casserole under your grill, preheat oven to 220C and bake soup uncovered until cheese is golden and bubbling.
This classic French dish is exactly the kind of hearty, warming fare you'd hope to find in an equally classic French bistro. There are plenty of red wines that fall into the classic bistro category - juicy, thirst-quenching young reds that also have enough substance and grip to help them stand up to the garlicky, rustic, cheesy food. Beaujolais springs to mind, and spicy syrah and grenache blends from the length of the Rhône Valley are also popular, but reds made from the cabernet franc grape, especially those from the Loire Valley, from appellations such as Chinon and Anjou, are all the rage in French bistro land at the moment, and it's not hard to see why. Cabernet franc tends to be juicier, lighter and more approachable than its sturdier offspring, cabernet sauvignon. There's quite a bit of cabernet franc grown in Australian vineyards, and although most of it is blended (usually with cabernet sauvignon, merlot, and petit verdot or malbec - the classic red Bordeaux mix), some producers do bottle it as a single-varietal wine. A good cab franc is lovely with this soup: the black fruit liveliness matches the cheesy perfume and sweetness of the onions, and the cab franc's dusty, sometimes even herbal, streak works with the rye bread.