Preheat the oven to 180°C.
Boil onions for four minutes, add sage for one minute, then drain.
Pulse onions, sage, breadcrumbs, 40g butter, yolk, and spices in a food processor.
Stuff chickens with the mixture and rub exterior with extra butter and seasoning.
Place chickens in a tin with 100ml water and cover with foil.
Roast for up to two hours, removing foil 20 minutes before finishing to brown skin.
Strain and reserve chicken juices for the sauce.
Dissolve sugar in 100ml water, add lemon zest, and boil for three minutes.
Poach gooseberries in the syrup for five minutes until tender, then cool.
Sieve gooseberries to create a smooth puree, reserving the syrup separately.
Reduce white wine by half in a pan over high heat.
Add 300ml chicken juices and reduce volume by half again.
Whisk in 25g butter, stir in gooseberry puree, and adjust seasoning with reserved syrup.