Preparation

• Blanch the watercress in a large pot of boiling salted water for about 2 minutes so that it is still bright green. Drain and rinse under cold water until completely cool, then squeeze to remove as much excess moisture as possible. Chop finely.
• Combine the cream, lemongrass, ginger, hot sauce and fish sauce in a large heavy-bottomed saucepan over medium heat. Cook for about 25 minutes to reduce the total amount to about 300ml. Strain the sauce through a sieve back into the cleaned pan.
• Add the blanched watercress, spring onion and coriander. Taste and add salt and/or pepper if needed. Cook for about 2 minutes to warm the sauce, then reduce the heat to low to keep it mixture warm.
• Prepare a bed of crumpled aluminium foil on a baking tray for the oysters so that they do not topple over during baking.
• Open the oysters using an oyster knife and place them on their half-shells, side-by-side on the crumpled foil. This can be done up to 1 hour in advance.
• Preheat the oven to 260°C.
• Spread a bed of coarse salt about 1cm thick on a large serving platter.
• Roast the oysters on the baking tray on the lowest shelf of the oven for 7-10 minutes, until their juices are bubbling and their edges begin to curl.
• Using a towel, transfer the oysters to the serving platter – the coarse salt will fix them in a horizontal position. Spoon a heaped tablespoon of the watercress cream sauce onto each oyster and serve.