French onion soup is all about achieving deep, rich flavors with technique and a relatively limited set of ingredients. There are many versions of the dish and some recipes are simpler than others. You should go with the simplest recipe you can find as this is one of those dishes that can be ruined by over-complication. That said, seasonings are important so here are some of the best spices for French onion soup:
You know onion is the most important ingredient in French onion soup because of the dish’s name. Its main flavor comes from the large portion of onions used in most versions. Sweet or yellow onions will work but yellow onions are the most widely recommended. The onions provide a strong, sweet caramelized quality that gives French onion soup its distinctive umami flavor profile.
The onions will have to be prepared properly by slow-cooking them for at least 40 minutes until they provide the right color and taste.
In many recipes, thyme is French onion soup’s lone herb. It provides a savory version of mint with mild bitterness and a camphoraceous quality that helps to balance out the onion’s sweetness. Thyme can be an aggressive flavor so it is usually added early in the cooking process so that it can mellow out by the time the dish is ready to be served.
You won’t see bay leaves in all french onion soup recipes, but they do show up in a few. They bring a deep savory note with a hint of bitterness to help enhance the umami aspects. You will need to add them early in the cooking process since they take extensive cooking to release their flavor. They don’t soften no matter how long they cook so you will need to remove them before serving the soup.
Another crucial ingredient in French onion soup, black peppercorns are the only true spice in the dish. Black pepper is a key element because it does provide a small amount of heat. For the true French onion soup experience, you will want to use fresh ground black pepper to get the full benefit of its spiciness and aromatic citrus notes.
Gruyere’s flavor is often described as rich, earthy and nutty. It’s technically not a spice but it is a key ingredient and responsible for much of French onion soup’s distinctive taste. Not only does it bring richness and a distinctive appearance to the soup, but it also adds a cheesy tang.
As in many French dishes, wine is an essential background note in the flavor profile. The wine in most French onion soup recipes is commonly either vermouth, port or a dry red. Wine contributes a little sweetness and tangy acidity to the soup that both complements and balances the onions.
After onions, the next most important ingredient in a French onion soup is the stock. It makes up most of the soup and provides a lot of its flavor. It is also largely responsible for the deep brown color of this soup. The stock is the key source of umami and the soup’s depth.
The traditional stock to use is beef stock. Ideally, you want to make it from scratch but this can be a long and arduous process for a home cook. A high-quality canned stock will do. Keep in mind that the quality of the stock will directly impact the quality of the finished soup.