Preheat the oven to 220°C. Lightly grease a medium baking dish.
Put the potato in a medium saucepan, cover with cold water and bring to the boil. Decrease the heat and simmer for 30 minutes, until tender. Peel the potato while still warm and mash well in a mixing bowl.
Add the meat, pecorino cheese, mortadella, egg, marjoram and garlic. Season with salt and pepper. Mix thoroughly.
Shape tablespoonfulls into firm meatballs, dust with flour and place into a tray.
Cut tomatoes in half. Secure tomato halves and meatballs with a toothpick. Arrange upright into a prepared baking dish.
Cook in the oven to 220°C for 5 minutes. Pour white wine and vegetable stock alternately around meatballs. Cook for another 25-30 minutes, until golden brown.
Serve warm. Share and enjoy.
