I have finally been given proper instructions on how to make a Gypsy tart by my friend, Donna. The secret is whisking. It didn't split, unlike the countless other attempts I've done.
Just keep whisking - you can't over mix this - I've whisked for 30 minutes before the sugar dissolved.
Any brown sugar will do, but not white nor demerara.
To make enough for one tart - 150g evaporated milk to 183g sugar.