Preheat oven to 180°C/350°F fanbake and line a large roasting dish with baking paper for easy clean-up.

To make the Tarragon Garlic Butter, place all ingredients in a food processor and whizz to combine.

To butterfly the chickens, use a sharp pair of kitchen scissors or shears to cut down the backbone of each bird (you can cut down both sides of the backbone and remove it, or just cut down one side and leave it in).

Place chickens skin-side up on a clean board and press flat with the palm of your hand until they form a butterfly shape. Spread the butter evenly over each of the chickens on both sides.

Place chickens skin-side up in the prepared roasting dish with the shallots and tarragon.

Roast until the chickens are golden, the juices run clear when they are skewered in the thickest part of the thigh and the liquids inside are brown not red (about 40-45 minutes depending on size).

Transfer to a board, cover with a clean teatowel and allow to stand for about 10 minutes before carving into portions.

Serve hot, warm or at room temperature with the cooked shallots.