Hi, Can anyone please give me a bit of advice on how to make a mandarin dessert sauce. I have searched countless recipe sites but can only ever find recipes for savoury dishes. I have no idea where to start creating one from scratch. Thanks

Maybe start with a marmalade recipe.  I would try cooking the mandarin down in a saucepan with some sugar to taste and maybe some complementary spices (ginger?).  If you need it smooth run it through a strainer, if not, use as is.