Melt 2 tablespoons butter in a saucepan over medium heat. Stir in shrimp shells; cook, stirring, until shells turn pink, 2 minutes. Pour in water and bring to a simmer; cook 20 minutes. Remove from heat and set aside.

Melt 2 tablespoons butter in a large saucepan over medium heat. Stir in green onions, celery, and jalapeno; cook, stirring, until mixture is slightly softened, about 5 minutes. Reduce heat to medium low, stir in flour and cook 3 minutes.

Pour tomato soup into onion mixture; stir to combine. Pour shrimp shell mixture through a mesh strainer into tomato soup mixture. Increase heat to medium-high and bring to a simmer.

Stir coconut milk, red curry paste, and fish sauce into tomato soup mixture, bring to a simmer and cook for 15 minutes. Stir in shrimp, decrease to heat to low and simmer until shrimp are cooked through, 3 to 4 minutes. Ladle bisque into bowls, place a rice cracker in the middle, and top the cracker with sliced basil.