1. With the rack in the middle position, preheat the oven to 350°F (180°C). Generously butter a 6-inch (15 cm) springform pan and line the bottom with parchment paper.
2. In a bowl, whisk the egg yolks, egg, sugar and salt with an electric mixer until pale.
3. In a small pot over very low heat, melt the butter. Remove from the heat. Add the chocolate and stir until melted. Gently stir into the egg mixture. Fold in the flour. Spread the batter out in the prepared pan.
4. Bake for 25 minutes. The cake will still be very soft at the centre but not liquid. Let cool completely on a wire rack, about 3 hours. Unmould on a serving dish.
5. When ready to serve, sprinkle with the cocoa powder. Delicious served with whipped cream or berry coulis.

CHEF’S SECRET

Use your favourite chocolate here: its flavour is what will really make this recipe shine. Sprinkle the cake with a pinch of fleur de sel once out of the oven for a salty-sweet touch.