Rub the inside of the Dutch oven with the cut garlic and then add the wine, brandy and lemon juice. Place over medium heat until the liquid hits 135 degrees F or just begins to steam.
While the liquid is heating, thoroughly toss the cheeses together in a large bowl with the cornstarch and the white pepper.
When the liquid hits 135 degrees F start stirring in the cheese, a handful at a time, using the spatula. Wait until the last addition is almost melted before adding the next.
When all the cheese is in the pot, increase the heat slightly and switch from the spatula to the whisk. Whisk constantly until the mixture lightens and is smooth. Add the horseradish and continue whisking until the fondue pours in a ribbon off the whisk and kind of coils up on the surface a bit like a rope before dissolving, about 5 minutes.
Remove from the heat, place the lid on the pot and take to the table. ***
Serve alongside bread chunks for dipping. I like to mix up torn and toasted pieces of sourdough, pumpernickel and challah. Some folks will tell you to serve vegetables -- whatever.
*I only say this because it's taken me a really long time to get this right. **This can also be done easily in a double boiler composed of a glass or stainless steel mixing bowl set over a pot of simmering water. If you go that route you'll need to serve it with the hot water underneath or the fondue will set up fairly quickly. ***Because it's cast iron, the pot should remain warm enough to keep the fondue pliant for about half an hour. If you want to keep it warm longer than that, consider nestling the Dutch oven in a bowl with a standard drug store hot pad set to high.