Shred and combine cheeses, toss with flour, set aside.
In fondue pot whisk together stout, cider, and Dijon mustard bring to a simmer.
Once liquid begins to bubble slightly around the edges start adding cheese to the pot stirring constantly, until all cheese has been added and fondue is a smooth consistency. You may need to thin it out with more stout if desired. Be careful that heat does not get too high; if you have an electric fondue pot keep at simmer. If using a sterno you may need to regulate the temperature with the snuffer.
Notes
Serve with roasted vegetables, bread chunks, and sweet gherkins.Note: Roasted vegetables can be made a day in advance by tossing potatoes/cauliflower/broccoli/onions/carrots in olive oil, sprinkle with salt and pepper, spread on a baking sheet and bake at 400 degrees for 20 minutes. Allow to cool and store in refrigerator until one hour before your ready to fondue. Vegetables should be room temperature.