Mix the ground almonds with the vinegar and a dash of cinnamon and set aside to macerate.

In a large pot, preferably of terracotta or enameled cast iron, braise the onions in a generous glug of olive oil with a pinch of salt, as gently as you can possibly manage, until they are well reduced, translucent and falling apart soft. Take care that they don't darken too much or burn as they braise; if need be, add a bit of water along the way to make sure. The whole process will take something like 45-60 minutes.

When the onions are done, add the macerated almonds and mix them into the onions. Let the onions and almonds sauté for a few minutes, then add the sugar or honey, and a good grind of black pepper, and sauté for a few minutes more.

When all the flavors have melded, add the broth and simmer the whole thing gently for about 3o minutes or so. Taste and adjust for seasoning.

To serve, lay a slice of toasted bread in the bottom of each bowl, then ladle over the onion soup. Top with grated cheese and, if you like, a sprinkling of cinnamon, sugar and/or a drizzle of olive oil. Serve immediately while the soup is still piping hot.