Place the Sadia Chicken Thighs in a large saucepan, cover with cold water and bring to a boil over medium heat. Reduce heat and simmer until the chicken is cooked. Drain the chicken, and allow to cool. Heat one tablespoon each of the oil and butter in a frying pan and cook the onion, spring onions, celery and garlic until very tender. Add to the mashed potatoes and keep aside to cool.
Remove the skin and bone from the chicken and discard. Shred the chicken and add to the potato mixture. Stir in parsley. Whisk the egg and mustard together and add to the chicken and potato mixture. Season well and combine the mixture with a fork. Shape into large balls, flatten slightly and coat with the breadcrumbs.
Melt the butter and extra olive oil in a large frying pan over medium heat. Cook chicken cakes until golden and hot in the centre.
Serve, garnished with rocket, tomato ketchup and sour cream.