I'm not a huge fan of curry, lemongrass or even Thai food in particular, but this soup, served for many years by the original owners of the Kona Inn Restaurant in Hawaii, is absolutely wonderful if you like things spicy and sweet. Many years ago, in what was either a mistake or the greatest act of corporate generosity ever, they answered our request for the soup recipe with the prep manual for the restaurant's entire menu. 
So here's the exact recipe which you will, at least at first
, need to scale down for home use. It's billed as "mildly spicy" on the menu, but the recipe has an amazing affinity for added heat: the restaurant usually serves it with the heat turned WAY up (to the point of causing sweat) and it's even more fantastic. Anyway enjoy!
THAI CURRY LEMONGRASS SOUP
YIELD: 52 CUPS/35 BOWLS (315 OZ)
INGREDIENTS:
48 OZ WHITE WINE
6 OZ LEMONGRASS STALKS, FINELY CHOPPED
3 LIMES -- ZEST ONLY
3 TBS GINGER, FINELY CHOPPED
3 TBS GARLIC, FINELY CHOPPED
138 OZ CLAM JUICE (3 CANS)
84 OZ COCONUT MILK (6 CANS)
3 TBS CURRY POWDER
8 OZ HONEY
1 1/2 OZ SARACHI CHILI SAUCE
8 OZ SWEET CHILI SAUCE
8 TO 16 OZ CORNSTARCH
METHOD:
1. ADD ALL INGREDIENTS INTO STOCK POT EXCEPT CORNSTARCH
2. REDUCE BY 1/4
3. MIX CORNSTARCH WITH ENOUGH WATER TO MAKE SLURRY
4. ADD TO SOUP SLOWLY AND COOK UNTIL THICKENED

So here's the exact recipe which you will, at least at first

THAI CURRY LEMONGRASS SOUP
YIELD: 52 CUPS/35 BOWLS (315 OZ)
INGREDIENTS:
48 OZ WHITE WINE
6 OZ LEMONGRASS STALKS, FINELY CHOPPED
3 LIMES -- ZEST ONLY
3 TBS GINGER, FINELY CHOPPED
3 TBS GARLIC, FINELY CHOPPED
138 OZ CLAM JUICE (3 CANS)
84 OZ COCONUT MILK (6 CANS)
3 TBS CURRY POWDER
8 OZ HONEY
1 1/2 OZ SARACHI CHILI SAUCE
8 OZ SWEET CHILI SAUCE
8 TO 16 OZ CORNSTARCH
METHOD:
1. ADD ALL INGREDIENTS INTO STOCK POT EXCEPT CORNSTARCH
2. REDUCE BY 1/4
3. MIX CORNSTARCH WITH ENOUGH WATER TO MAKE SLURRY
4. ADD TO SOUP SLOWLY AND COOK UNTIL THICKENED