Place whole oranges and grapefruit (skin on) into a large saucepan and cover with water. Bring to a boil, cover with a lid, and turn to simmer for 1.5 hours (Check every now and then to ensure fruits are always covered with water, topping up the pan with boiling water if required).

Drain oranges and grapefruit, reserving 400ml of the cooking liquid.

Once cooled, cut into quarters and remove any pips. Use a spoon to scrape the pulp from each piece and set it to the side.

Thinly slice the remaining orange and grapefruit peel.

Combine orange and grapefruit pulp, sliced peel, reserved 400ml cooking water, lemon juice, and sugar in a saucepan, stirring over low heat until all the sugar has dissolved, then bring to a boil and bubble rapidly for 15- 25 minutes or until setting point is reached (approximately 105°C)

Take the pan off the heat and stir gently to combine. Leave the marmalade to stand in the pan for 20 minutes to cool a little and allow the peel to settle. To finish, pour in gin, vermouth and Campari and stir gently to combine.

Transfer negroni marmalade to sterilised airtight jars. Refrigerate for a minimum of 4 hours or preferably overnight to allow the jam to set.