Preheat the oven to 180°C, fan 160°C, gas 4. Melt half the butter in a pan and cook the onion and garlic for 5-10 minutes. Add the chestnuts, cranberries and the remaining butter and cook for a further 5 minutes.
Transfer to a bowl, then stir through the herbs, breadcrumbs and beaten egg. Use a fork to mix well, then leave until cool enough to handle.
Roll into 16 balls, then place on a baking parchment-lined baking tray. Cook for 15-20 minutes until golden, then serve with the Christmas turkey.