Preheat the oven to 190° C w/ fan.
Line a baking tray w/ baking parchment.
Clean & trim the Brussels sprouts.
Mix the Brussels sprouts w/ olive oil & salt & pepper & arrange the brussels sprouts on the baking tray.
Roast in the oven for about 20-30 min until brown, crispy & soft; put aside.
Reduce the oven temperature to 160° C w/ fan.
In the meantime: Grate the Gruyère.
Fry the chopped spring onions & the bacon in some olive oil.
Oil the springform.
Mix the quiche dough w/ water, knead it & roll it out large enough to cover a springform bottom & its edge.
Fill in the Brussels sprouts for 1 layer on the bottom.
Mix crème fraîche & eggs w/ an egg whip.
Fold in the grated Gruyère.
Fold in the fried spring onions & the bacon.
Pour the mess into the springform.
Bake at 160° C w/ fan for about 45-55 min.
Let it cool for 5-10 min & open carefully the edge.
Transfer to the final plate when cooled down.