Peel the orange and lemons, taking care to avoid getting the white pith, which is bitter. Then juice them.
Measure the wine, water, sugar, and citrus juice into a large saucepan or stock pot.
Add the citrus peel, cloves, nutmeg, cinnamon, and bay leaves to a bouquet garni muslin bag and place it into the saucepan.
Heat the mulled wine gently, stirring to dissolve the sugar. When it starts to steam, turn the heat off and let it infuse as it cools. Do not let it boil.
To serve, pour a splash of brandy into each glass (optional) and add a slice of orange. Reheat the mulled wine to a warm (but not boiling) temperature and serve.
Notes
A glass serving jug is better at insulating mulled wine and keeping it warm than a plastic one.