French Onion Soup

6 yellow onion, thinly sliced

2 thyme, sprigs

1 baguette, sliced into 1-inch thick rounds

60 g unsalted butter

150 g gruyere cheese, grated

15 g all-purpose flour

120 ml red wine, dry, such as Pinot Noir

1 L beef stock, preferably low-sodium

5 ml kosher salt

2 ml black pepper, freshly ground

1 bay leaf