1) Pour stout into a medium pan and heat over medium heat.
2) Once stout is steaming, start whisking in port wine cheese in 3 batches. Once one batch is melted, add the next one.
3) Whisk the cheese regularly. It might look as if it is separating but eventually it will melt together with the stout and form a smooth dip.
4) Add nutmeg and turn heat down to medium-low.
5) Continue to simmer until fondue thickens, about 10 more minutes. Serve immediately with cubes of crusty bread. It reheats really well also.