Position a rack in the middle of an oven and preheat to 350F. Butter a springform pan9 inches in diameter and 3 inches deep. Line the pan bottom with a piece of parchment paper cut to fit Precisely.

In a heavy saucepan over medium low heat, combine the chocolate and butter. Heat, stirring, until the mixture is smooths removes from the heat and let cool Whisk in the vanilla.

In a large bowl, combine the eggs and sugar. Using an electric mixer set on medium-high speed, boat until the mixture lightens and triples in volume, about 6 minutes. Pour the chocolate mixture over the egg mixture. Using a rubber spatula, gently fold them together. Pour the batter into the prepared pan.

Bake until the top forms a crust and cracks and a toothpick inserted into the center comes out with some wet batter attached, about 45 minutes. Transfer to a rack. Limnediately run a knife around the pan sides to loosen the cake; it will fall in the center. Press down on the edges to even the top. Let cool

Release the pan sides and remove them. Trim off any crumbly edges. Invert a flat plate over the cake and invert them together. Lilt off the pan bottom and peel off the parchment paper. Tuck strips of waxed or parchment paper under the edges of the cake and pour the lukewarm glaze over the cake top; use an icing spatula to coax it down the sides. When the glaze stops dripping, remove the paper. Refrigerate until the glaze sets, about 1 hour.

Serve immediately, or cover with a cake dome and refrigerate for up to 1 week. Serve cold or at room temperature.

Serves 12. Makes one 9-inch cake.