My Dad and I used to catch small perch at the local harbor for Gingery Mustard Greens and Tilapia Soup (Canh Cai Ca Ro). Amid the sailboats and cabin cruisers, we would lower our poles, the lines baited with thawed frozen peas, to catch the three- to four-inch-long fish, the American equivalent of Vietnamese cá rô. We would bring home about a dozen fish, and my mom would gut them for this classic Viet combination of sweet fish, sharp mustard greens, and ginger.
One day, Mom protested that cleaning the fish took too much time, so we stopped catching them, and the soup didn’t grace our table for years. On a trip to Vietnam, I saw a fishmonger at Ben Thanh market in Saigon cleaning cá rô, which reminded me of how good Gingery Mustard Greens and Tilapia Soup (Canh Cải Cá Rô) is. Back home, I decided to use whole tilapia, which is sometimes identified as cá rô in Viet markets. It worked just like traditional cá rô in Vietnamese cooking, but its larger size made it much easier to prep and cook. Now, this brightly flavored Vietnamese soup is back on my table as an ideal balance for bold, rich foods like Vietnamese-Style Grilled Lemongrass Pork Riblets. Whole tilapia is sold at Asian and Latin markets.
FRAGRANT AND SOFT ONIONS
The soups, as well as many other Vietnamese Soup Recipes, include gently cooking onions until they are fragrant and soft. This unhurried step is called phi hành and takes about four minutes to complete over medium heat.
The purpose is to coax the sugars from the onions without browning them. You know the onions are ready when you stick your nose over the pan and the harshness of onion has been transformed into a sweet aroma. The onions will have lost their opacity and turned translucent, and they will have lost all their crispness and become limp. Note that phi hành shouldn’t be confused with the crispy fried shallots called hành phi.
DUELING SOUP PHILOSOPHIES
There are two schools of canh making: the drop-into-boiling-water school and the sauté-first-then-simmer school. Cooks who follow the former practice argue that their method produces a pristine, clear broth. I prefer to extract extra flavor from some of the ingredients, such as onion, by sautéing them first and then adding the seasonings and water. A brief simmer follows and the soup is done.
The broth is not quite as clear as with the drop-into-boiling water method, but the flavors are stronger.