Preheat the oven to 190°C. Wash the Sadia Whole Chicken thoroughly, inside and out, in salted water and dry with a kitchen paper towel. Remove the neck and discard.
Heat the olive oil and 2 tablespoons of the butter in a frying pan over medium heat. Add the onion and cook for 5 minutes, until softened. In a large bowl, combine the onion mixture with the breadcrumbs, pistachio and raisins. Season with salt and pepper.
Place the chicken on a board and carefully slide your fingers underneath the skin between the breast and legs; spoon in the stuffing. Spoon the remaining stuffing into the neck cavity and secure with a toothpick. Tie the legs together with kitchen string and fold and tuck the wing tips under the chicken.
Place the chicken in a small roasting pan. Smear the remaining butter; squeeze the lemon juice over the chicken and season with salt and pepper. Roast for 1-1½ hours, until the juices run clear when a skewer is inserted into the thickest part of the thigh. Lift the chicken from the pan and place on a plate and keep warm.
To make the gravy, remove the excess fat from the roasting pan. Place the pan over medium heat and whisk in the flour, stir in the chicken stock and cook until thickened. Serve the chicken with the gravy and vegetables of your choice.