Pour the thick creamy top half of the coconut milk into a large pot, bring to boil on medium heat, and stir in the curry paste. Fry, stirring constantly, until aromatic, darker in color, and oily on the surface.
Add diced pork, lemongrass, and lime leaves, and stir as the pork begins cooking, adding coconut milk a couple of tablespoons at a time.
Add pumpkin with the remaining coconut milk, season with fish sauce and sugar.
Simmer, checking regularly, until pumpkin is cooked but not mushy.
Stir in basil leaves, chilies, and lime juice and remove from heat.
Serve with steamed rice, garnished with basil.
Tips: For a less creamy sauce, add some water and adjust seasonings. For a vegetarian dish, use green beans instead of pork.