Preheat the oven to 450 degrees F/230 degrees C.
Spread the creme fraiche over the pastry
, going all the way out to the edges. Scatter the onion slices and bacon over the creme fraiche. Grind some pepper on top and sprinkle with fleur de sel
. Bake until the creme fraiche is bubbling, the bacon is cooked and the onions
are curled and starting to brown, about 20 minutes.