What I've heard about this recipe is it was created by Chef Joel Robachen of Jamoin in Paris for Valrhona Chocolate Company. He taught it to Jean-Georges Vongerichten and I learned it from one of his sous chefs who worked for me in London at the Criterion Brasserie. It's basically an under baked cake sp the batter is just raw in the center, though when I worked at Charlie Trotter's we placed a thin layer of chocolate sponge cake on the bottom and placed on that balls of ganache to stuff in the center to assure a wet lava effect when you cut into the cake, then surrounded the whole thing with the cake batter.
1. The success of this 'oozy' cake hinges on precise baking; the center should be molten, not raw or fully set. Watch closely, as ovens vary. 2. For an even more reliable 'lava' effect, consider the advanced technique mentioned: placing a thin layer of chocolate sponge on the bottom and embedding a small ball of ganache in the center of the batter before baking. 3. Use high-quality bittersweet chocolate (60-70% cocoa) for the best flavor depth. 4. Ensure butter and chocolate are melted gently over a double boiler to prevent scorching. 5. Serve immediately after unmolding to experience the full molten effect with the recommended accompaniments.