To make the crêpe batter, begin by sifting together the plain and buckwheat flour and salt into a large bowl. Make a well in the middle and gradually add milk, water and eggs together. Mix until all the flour is incorporated, then add melted butter and leave to rest.
For the filling:
For the filling, melt butter in a saucepan and add onions. Stir well, cover and leave to sweat over very low heat for about 20 minutes. Add a splash of water if the onions start to brown. They should be soft, but not coloured. Add cream, season, and set aside.
In a large oiled frying pan, add some of the batter and swirl around the pan around to make large and thin crêpes.
Cook eggs in a separate pan to your liking.
Cover each crêpe with bacon, onions, cheese and eggs and fold over. Serve immediately.