Boil the potatoes whole and then let them cool in the fridge.
Slowly sweat down the onions, garlic and salt in a little butter or oil in a frying pan until caramelised.
Turn on the oven and heat to 180°
Slice the cooled potatoes into ½ cm thick.
Grease a baking dish (I use an enamel baking dish for the best results.
Layer the potato and onion until you reach the top of the dish making sure you end with a layer of potato.
Blended the coconut cream. Eggs and mustard together and then pour the mix over the layered potato and onions. For a vegan version simply don't add the eggs.
Pop the dish in the oven and cook until firm and golden brown on top.