Line a large baking tray with a sheet of non-stick baking paper.
Place the potatoes in a medium saucepan of salted cold water. Partially cover with a lid and bring to the boil over a medium heat. Take care not to let the water boil over. Reduce the heat and simmer for 20 minutes, until tender.
Drain the potatoes well and return them to the saucepan off the heat. Cover with the lid and leave for a couple of minutes. Using a potato masher, mash the potatoes until smooth.
Stir in the egg yolks, Parmesan, garlic granules, chives and season with salt and black pepper if needed.
Place the mixture in a piping bag fitted with a 2 cm (¾ inch) star nozzle. You may need to do this in 2 batches. Pipe 5 cm (2 inch) diameter swirls onto the lined baking tray, leaving gaps between each.
Place in the preheated oven and bake for 15 minutes until golden brown. Serve hot with a main course of your choice.