To make the sweet fish sauce dressing, pound the garlic, chilli, sugar and a pinch of sea salt together in a large mortar. Add the fish sauce and lime juice, mix well and set aside.
To make the thickened coconut dressing, heat the vegetable oil in a saucepan over a medium heat.
Add the spring onion and saute for 30 seconds. Add the coconut cream, cornflour mixture, palm sugar and a pinch of sea salt. Stir for 30 seconds, until the mixture comes to the boil and thickens slightly. Remove from the heat and set aside.
Soak the dried shrimp in a little boiling water for 5 minutes, then drain. Pound the shrimp in a mortar until it begins to break down. Set aside.
Meanwhile, cook the noodles in a saucepan of boiling water for 2 minutes, then remove the pan from the heat and stand the noodles in the water for 5 minutes. Drain well, rinse under cold water, then drain well again.
Divide the lettuce, bean sprouts, cucumber and herbs among four individual bowls. Top with the noodles, then the shrimp, and then toss the salads separately.
Add 2 tablespoons of the sweet fish sauce dressing and 2 tablespoons of the thickened coconut dressing to each bowl. Garnish each with the peanuts and serve.