Roughly chop the onion and celery and add to the Instant Pot with the halved garlic cloves.
In a bowl, zest the orange and combine with the juice from just one half of the orange.
Chop the squeezed-out halve of orange and add to the pot, then place the gammon joint in too, on top of the onion, celery and orange.
Pour over the carton of orange juice, cloves, bay leaves, cinnamon stick, peppercorns and enough water to come 3/4 of the way up the gammon.
Select Pressure Cook Manual High and programme for 35 minutes.
Whilst the gammon is cooking place the freshly squeezed orange juice and zest mix into a small pan and heat until bubbling. Once it has reduced, remove from the heat and stir in the cinnamon, and then the brown sugar.
Carefully remove the remaining pith from the other half of the orange and slice thinly.
Once the pressure cooking has finished, allow for 5 minutes of Natural Pressure Release, then remove the gammon from the pot and discard the liquid.
If using the Duo Crisp, place the trivet into the pot, and put the gammon back inside on top. Glaze the meat with the orange sugar syrup and place the Air Fryer Lid on and programme Roast at 195℃ for 15 minutes. If you’re not using a Duo Crisp, place into a preheated oven or a Vortex Air Fryer instead at 193℃ for 15 minutes.
Add the orange slices to the top of the gammon after 7-8minutes, and then continue to cook for the rest of the time until the top is crispy.