Begin by butterflying the prawns: run a sharp knife down the back of the prawn and gently open out slightly. Don’t worry, it doesn’t have to be perfect - you just want to give them more surface area.
Pat the prawns dry on some kitchen paper, then add to a bowl. Season with salt and pepper. Sprinkle over the paprika and toss gently to coat. Add a glug of oil and add the zest of 1/2 lemon. Set aside.
For the herby sauce: add all the ingredients to a blender with a good pinch of salt and crack of pepper. Blend until smooth.
Add the butter to a large non-stick frying pan and set over medium heat (if you don’t have a large enough pan, cook in batches). Swirl until melted and sizzling. Add the garlic and sauté for about a minute, stirring to ensure it doesn’t catch and burn. You don’t want the garlic to take on any colour.
Add the prawns to the hot butter and cook for a couple of minutes, stirring occasionally, or until they turn pink. Watch closely as you don’t want them to overcook or they will become rubbery.
Remove from the heat and add the lemon juice, to taste. Sprinkle in the chopped parsley and dried chilli flakes, to taste, then stir to coat.
Spoon into bowls and serve with your choice of side (see Notes).