These grilled prawns with bloody mary butter appear in my latest cookbook, Margaret and Me. Check out the video of me cooking these gorgeous numbers with my grandmother Margaret Fulton. Inspired by the flavours of New Orleans, these are simple to do in a pan or the barbecue, and you can make the green oil ahead, then just do the grilled prawns as you like. Here's the recipe!

Grilled prawns, bloody mary butter & green oil

• 12 large raw king prawns
• 1 handful watercress sprigs lime wedges, to serve

Bloody Mary butter

• 60 g (2¼ oz) butter, softened
• 1 garlic clove, finely chopped
• 2 tsp Tabasco or hot sauce
• 1 tsp sweet paprika
• 1 tbs tomato paste (concentrated purée)
• 1 tsp Worcestershire sauce pinch of sea salt

Green oil

• 250 g (9 oz/2 large bunches) curly parsley, leaves picked
• 60 ml (2 fl oz/¼ cup) extra virgin olive oil

For the green oil, bring a medium saucepan of salted water to the boil and have ready an ice-water bath. Add the parsley leaves to the boiling water, cook for 20 seconds until bright green, then drain and quickly transfer to the ice bath to stop the cooking process. Drain, then put the parsley in a food processor or blender and blend until smooth.

Pour the parsley purée into a muslin-lined sieve placed over a jug or bowl and allow the juice to drain into the bowl for 5 minutes. Squeeze the puréed leaves gently to extract more juice, then discard. Add the olive oil to the parsley juice, season with salt and whisk together. Set aside.

For the Bloody Mary butter, combine all the ingredients in a bowl and mix well. Season with sea salt and freshly ground black pepper.

Using a sharp knife, cut the prawns and heads in half lengthways, taking care not to cut all the way through – they should still be joined along the centre back. Open out the prawns and remove the gastrointestinal tract.

Using a pastry brush, brush the prawn meat with half the Bloody Mary butter.

Heat a barbecue or chargrill pan to high and cook the prawns, meat-side down, for 1 minute. Turn them over, brush with the remaining butter, and cook for a further 30 seconds, until just cooked.

To serve, arrange the prawns on a serving platter, drizzle with the green oil and scatter with watercress sprigs. Offer lime wedges for squeezing.

You can make the green oil in advance and store in a jar or airtight container in the fridge for up to 1 week.