Flatten the fillets using a wooden mallet

Finely chop the parsley and coriander

Place into a bowl together with the feta and harissa

Blend together using a fork

Season the fillets and place the herb mixture on top

Roll tightly into a sausage shape using cling film

Tie knots at each end and place the ballotines into a sous vide bag

Vacuum seal and place into a sous vide cooker set at 65º Celsius

Cook for 1.5 – 4 hours

Heat some butter in a frying pan

Remove the ballotines from the cooker and cling film

Flash fry in the butter to add colour

Cut in half and serve