Grilled Prawns With Tom Yum Sauce

Make the sauce. Heat a medium saucepan over medium heat. Add the shrimp heads and cook, stirring, until aromatic, 3 to 5 minutes. Add the lemongrass, galangal, makrut lime leaves and bird’s eye chile and cook, stirring until fragrant, about 5 minutes. Add chile paste, salt and cream. Increase heat to high and bring to a boil. Reduce heat to medium low and simmer until the flavors have melded, 30 to 40 minutes. Add the cornstarch and water mixture and stir until the sauce coats the back of a spoon. Strain through a fine sieve, pressing the solids to extract as much of the liquid as possible. Discard the solids and stir the sauce to blend completely. Makes about 1 1/2 cups of sauce.