Preheat the oven to 180C.
Season the chicken drumsticks and place in the oven, roasting for around 25 minutes. Remove from the oven, leave to cool for a few minutes and then shred the meat from the bone. Leave the shredded meat to one side while you prepare the roux.
In a heavy based saucepan caramelise the thinly sliced onions on a low heat for around 20 minutes, until golden, soft and translucent.
In a separate saucepan, melt the butter, add the flour and slowly add the milk, whisking it all together. Add in the grated cheese. Continuously stir the white sauce until all the milk has been absorbed and you have a thick, smooth sauce.
Take the bowl of pulled chicken and add the golden caramelised onions along with the mustard, and mix well. Pour over the white sauce and give it all a further mix. Season to taste. Place the bowl in the fridge for at least an hour to allow the mixture to set.
Remove the chicken mixture from the fridge, taking out a spoonful at a time, roll into ping pong sized balls until you have used up all the mixture.
Take three bowls, in one add some flour, the next add a beaten egg and finally the last pour in some breadcrumbs.
Toss the balls of chicken mixture in the flour, then into the egg and finally into the breadcrumbs.
In a deep frying pan pour in the oil, heat to around 180C. Place the croquettes into the oil and cook for approximately 4 minutes each, or until they are crisp and golden.
Serve piping hot with a little spiced chutney.