Disolve the yeast in the water and add salt, sugar, and oil.

Add the flour gradually, you might need to use a little more or less flour - you'll have to test it out. The dough should be smooth and slightly moist without being wet and sticky.

Place a damp cloth or a shower cap over the bowl and let the dough rise for about 30 minutes.

After the rising, take the dough out of the bowl and shape it into four round buns.

Let the buns rise for another 15 minutes.

With a small sharp knife, cut around the top of the buns where the lid should be. This will ensure that the buns rise in height during baking, rather than becoming flat and dense.

Dust the buns with flour and bake them for 5 minutes at 250 degrees Celsius (482 degrees Fahrenheit), then for 10-15 minutes at 200 degrees Celsius (392 degrees Fahrenheit).

Let the buns cool on a rack, they should be almost cool before you hollow them out and fill them with soup.

Cut the onions in half and then into thin slices. If using garlic, chop it finely.

Melt the butter in a pot, and add the onions and, if desired, the garlic. Sauté the onions over medium heat; they should become soft and golden but not brown and burnt, as they will then acquire a bitter taste.

Add the flour and stir until it is absorbed.

Add the broth and let the soup simmer over low heat for about 30 minutes. This takes about the same amount of time as the dough for the bread lids to rise.

Season the soup with salt, pepper, sugar, vinegar, and lemon juice.

Cut the top off the buns, following the cut you made along the edge. Hollow them out by removing the bread crumb, using a spoon if necessary. Remove enough to make room for the soup, but not so much that the "wall" becomes too thin and the soup seeps through the bread.

Fill the buns with soup and sprinkle the surface with grated cheese.

Place your bread bowls in the oven at 225 degrees Celsius (437 degrees Fahrenheit) and gratinate them until the cheese is golden - this takes about 10-15 minutes.

Serve immediately!