Chop the rhubarb and apple into chunks and add to a large pan. Add all of the other ingredients and bring to the boil. Simmer for around 30minutes until the chutney has reduced and thickened. Let it cool and store in a sealed container in the fridge until needed.
In a large bowl, place all the ingredients for the pork burgers and combine well with your hands. Place in the fridge for one hour to let the flavours develop.
Divide the mixture into four. Using a chef's ring / circular cookie cutter mould the pork into burgers. Use a plate and place the chefs ring in the middle. Add some pork mixture and press it flat and up to the insides of the ring to create thin burgers. Repeat until you have four patties and place in the fridge for at least 30minutes.
Heat a glug of oil in a large frying pan over a medium high heat. Gently add the patties in using a spatula to keep the burgers from breaking. Fry for around 10 minutes on each side until dark brown and cooked all the way through. Flip occasionally. Leave to one side.
Cut the brioche buns in half and place them cut side down in the burger frying pan and fry until nice and crispy.
Spread some mayo on the cut sides of the buns and layer the burgers and cheddar cheese slices and finish with a generous dollop of rhubarb and apple chutney
The ingredient amounts for the rhubarb and apple chutney will allow you to make a good jarful to keep in the fridge for a later date - it works great with a cheeseboard! If you want to make the chutney just for the burger, reduce amounts by 3/4