Thaw the puff pastry. Peel the bananas, cut in half lengthways and drizzle with lemon juice.
Preheat the oven to 200 ° C. Place one half of the banana diagonally on a sheet of puff pastry. Fold two opposite corners together over the bananas and press firmly. Brush with whisked egg yolk.
Bake on a baking tray lined with baking paper for 20 minutes. Let cool down.
Melt the couverture and garnish the pieces with it.