Preparation of the caramelised onion: Heat the butter in a saucepan with a pinch of sugar, allow to caramelise slightly and then add the julienned onion; keep over high heat for 2 hours, stirring from time to time.
Cut the goat's cheese into strips. Toast the bread, add a layer of cheese strips, place the onion on top and gratinate.
Presentation: Serve the toast with blueberry jam, raspberry jam and decorate with red berries.