Classic French Chocolate Moelleux Cake

Steps

1. Preheat oven to 350°F (180°C) with a rack in the middle. Grease an 8 or 9-inch springform pan with butter and dust with flour or cocoa powder.
2. In a medium bowl set over a bain-marie, melt the chopped chocolate with the butter. Once melted, let cool for 10-15 minutes.
3. In a large bowl, whisk half the sugar (100g) with the egg yolks until pale and foamy.
4. Pour the melted chocolate and butter into the yolk mixture while whisking. Add the cornstarch and whisk to combine.
5. In a separate large bowl, beat the egg whites with salt to stiff peaks. Gradually add the remaining sugar (100g) while beating.
6. Fold about a quarter of the egg whites into the chocolate mixture until just combined. Gently fold in the remaining egg whites in three or four additions; the batter should be airy and jiggly.
7. Pour the batter into the prepared pan. Bake for 25-30 minutes, until puffy with set edges and a slightly wobbly center.
8. Transfer to a cooling rack and let cool at least 15 minutes before removing from the pan; the cake will deflate and the top will wrinkle as it cools.
9. Serve slightly warm for a melty texture, at room temperature for a soft texture, or chilled for a firmer texture.