4 cups stock (vegetable or shrimp)
1 large handful kaffir lime leaves
4" chunk galanga root, hacked into thick slices if possible
4 stalks lemongrass, peeled of tough outer layers, cut into chunks and whacked with knife to bruise
1 can coconut milk
juice of 2-3 limes
2-4 Tbsp fish sauce
1-4 Tbsp Thai roasted chili paste (Nam Prik Pao), or other Thai chili paste or red curry paste
1 pinch-1 Tbsp sugar
1/2 lb mushrooms, sliced in halves or quarters, depending upon size
1/2 head cauliflower, broken into florets
2 small broccoli crowns, broken into florets
3 shallots or 1/2 red onion, thinly sliced
1/2 cup grape or cherry tomatoes, if it's the season
1 large handful mint leaves (optional, but nice)
1 lb shrimp, peeled
1/4 cup cilantro leaves, coarsley chopped
rice for serving (preferably sticky rice or jasmine rice)
In a large soup pot, combine the stock with the lime leaves, galanga root, and lemongrass. Bring to a boil, then reduce the heat until it's just enough to maintain a simmer. Simmer for 30 minutes to infuse the broth with the flavorings.
After 30 minutes, pour in the can of coconut milk. Add the lime juice, fish sauce, chili paste, and sugar, starting with the smaller amounts and tasting until you like the balance of hot, sour, salty and sweet flavors. The soup will be served with rice, so you can go a little heavier with the heat than you might otherwise. Add the mushrooms, cauliflower, and broccoli, and simmer for a couple of minutes, until a little shy of tender-crisp. Add the shallots or red onion, tomatoes (if using), and mint leaves, simmering another minute or two until the vegetables are just shy of done. Add the shrimp, and cook another minute until pink (they'll continue to cook in the residual heat, so err on the side of underdone). Turn off the heat.
Taste again to finally adjust the seasonings, add more lime juice, fish sauce or chili paste if needed. The inedible lime leaves, galanga root and lemongrass can be fished out, or left in to further infuse (just make sure diners know to set them aside as they eat). Serve in bowls with rice, topped with the fresh cilantro.