These people...
...who do this.
It's more than one of my favourite things at a festival, it's one of the highlights of my entire year. Their presence has been known to influence which festivals I attend. One of my greatest festival moments was persuading them as they were closing one night to sell me a load of the burned / caramelised cheese from the bottom of one of the pans they were scraping out.
Have tried recreating it myself, and I can get the tartiflette right (best with unsliced smoked streaky from sandridge farm), but I've never been able to crack the awesome, fatty-yet-lean garlicyness of the sausages they slow cook in wine. Closest I've got are some fat sausages from an italian deli, but they're not quite right.
FWIW, I cook my tartiflette with no onions, lots of reblochon and a fuck ton of double cream. To counter this, I only allow myself to cook it once per year.