Sooo good! I have made this for dinner parties a few times and have been asked for the recipe every time and am now asked to bring this dish specifically. I substituted Edam and Asiago cheese instead of the Gruyère. I also added more garlic, but I usually do to most recipes. I also never peel my potatoes. I love that the flavours of the cheeses make up for there not being a lot of it.
Delicious... a couple of things... cause I'm a tweaker (though this is one recipe that is pretty solid on its own):
1) Didn't peel the potatoes cause I forgot... came out fine
2) Put the used garlic halves in the milk to infuse the milk with garlic flavor
3) Used a bit more cheese, though not sure if it was necessary
4) I made the day before and just reheated it, my guests didn't know, and it saved me from running around like a crazy.