1. Fire up your oven, aiming for 180°C on the stone baking board.
2. Place your cast iron skillet in the oven and preheat to 180°C.
Remove the pan and add the butter. When it turns brown, add the herbs, swishing the sprig around the pan. Add the garlic and cook outside the oven for a few minutes.
3. Add the cheeses and cook in the oven for 2 minutes.
Remove the skillet and add the wine or beer, then return to the oven for another 2 minutes. The mix will feel loose, but don’t be tempted to overcook! (If you do, you’ll end up with a solid mass of cheese, rather than a lovely, creamy dip.) It will firm up on its own outside of the oven.
4. Remove the skillet and, if you wish, transfer to smaller dipping bowls to share.
Serve immediately with chunks of bread or focaccia. Fondue is a great way to make use of stale bread, but fresh will taste equally delicious.