Turning Up the Heat in Taste and Temperature Fred R. Conrad/The New York Times WHENCE comes this soup, you may ask. Inspiration is often whimsical. I was basically of two minds when I put it together, with just a craving and no real recipe to guide me. For one, with the onset of cold weather, having already endured a storm or two and with predictions looming for a long frigid winter, I had a short-lived fantasy of a holiday in a warmer clime. Perhaps Southeast Asia? That dream was only momentary (and not even remotely possible), which led me to seek comfort in a bowl of soup at home. This reality intersected nicely with my inclination, after all that Thanksgiving feasting, to eat on the lighter side for a while, while gearing up for the holidays on the horizon. It turns out that this Vietnamese-inspired soup actually tastes as good in the blustery city as it does in flip-flop country, so even without sunshine, it satisfies on both counts: it has the spicy, brothy flavors I wanted (without shelling out for airfare) and a light and healthy profile. Here's the part where whim comes in. I love the beefy goodness in a great big bowl of pho, but it takes hours to make a good beef broth. And at the time, I happened to be ogling seafood at the fishmonger's. Couldn't I make a similar soup, and a lot more quickly, with fish? There are a lot of great Vietnamese fish soups. With dinner guests on the way, there really wasn't time to research it, though, and the rich coconut milk versions I knew didn't qualify. So I decided to fake it, ad-libbing with ingredients like star anise and lemon grass, and using mussels and squid. That's what makes this dish "almost authentic," I suppose. The ingredient list for the recipe is rather long, but don't let that be intimidating. Most of the items are just the aromatics, which simmer together to give the soup its bright, complex notes, and they achieve it in well under an hour. The soup base can be prepared and the rice noodles can be soaked ahead of time as well. Adding the mussels and squid takes mere minutes just before serving. The most important part happens at the table. When you serve the big, steaming bowls of fragrant soup, pass a dish of finely slivered red or green Thai bird chiles. They are diminutive yet very potent. Whether you add just a tiny bit or opt for extra spicy, the chile flavor is essential. A big squeeze of lime pulls it all together.