How to Make It
In a medium saucepan, combine the sugar with 1 tablespoon of water. Cook over moderately high heat, swirling the pan, until an amber caramel forms, 4 to 5 minutes. Remove from the heat and immediately add the fish sauce, soy sauce and 2 tablespoons of water.
Heat a large skillet over high heat until smoking. Add 1/2 tablespoon of the canola oil and stir in half of the garlic and crushed red pepper; season with salt and pepper. Add half of the shrimp in an even layer and cook over moderately high heat, turning once, until the shrimp are crisp on the outside and just white throughout, about 3 minutes. Transfer to a plate. Repeat with the remaining oil, garlic, crushed red pepper and shrimp.
Return all of the shrimp to the skillet; add the caramel sauce. Cook over high heat, tossing, until the shrimp are hot and evenly coated, 1 to 2 minutes. Scatter the watercress on a platter, top with the shrimp and sauce and serve. Eat the shrimp with or without the shells.