Pour the port or sherry into a medium saucepan.
Whisk in the sugar a little at a time until the sugar is mostly dissolved.
Sift in the flour and whisk until it’s incorporated, then stir in the chocolate.
Set the saucepan over medium heat and bring it to a simmer, whisking constantly.
Continue to whisk and simmer it, reducing the heat if it starts bubbling too much, for 10 more minutes.
Remove the saucepan from the heat and let it sit, stirring occasionally, until it’s cool enough to drink.
It will thicken a bit more as it cools and will form a skin if you don’t stir once in a while.
Serve it forth warm in wine glasses or mugs.
