Melt the butter in a large (5-quart) pot over medium-high heat. Add the carrots and onion, season with a couple good pinches of salt, and cook, stirring often, until the carrots are softened, 15-20 minutes. Stir in the broth, 1 ½ cans of the coconut milk, and 1 tablespoon of the sriracha. Bring to a simmer, and cook, stirring occasionally, until the vegetables are very soft and the liquid is slightly reduced, about 45 minutes. Puree in small batches (remember: hot liquids expand!) in a blender. (Or, my preference: puree right in the pot, with an immersion blender.) Check for seasoning, and add more salt and/or sriracha, if you like. (I usually add 1 more tablespoon sriracha.) If you’d like more richness, stir in the rest of the coconut milk, and then reheat as needed.

Serve with a generous squeeze of lime in each bowl, and top with cilantro, if you have it.