Directions: Cake - In a double boiler, melt together the chocolate and butter until smooth. Remove from heat and stir in the sugar. Add the egg yolks to the chocolate one at a time, whisking well after each addition. Whisk in the flour, cocoa powder and vanilla. Beat the egg whites until stiff and add the 1/4 cup sugar. Folk in 1/4 of the egg whites, the fold in the remaining egg white mixture to lighten the batter. Spray an 8" square baking pan with non-stick spray and pour batter in pan. Bake at 350 degrees for 40-45 minutes or until tooth pick comes out clean. Cool completely. The cake will sink while cooling.
Sauce - In a small sauce pan combine the sugar, corn syrup and water. Place over medium heat and bring to a boil, stirring to dissolve sugar. When mixture comes to a boil, stop stirring and allow the mixture to boil until it becomes a golden caramel color. Remove from heat and add the butter and vinegar. Let butter melt and add the heavy cream and vanilla. Place back onto heat for 1 minute, stirring to combine. Cool sauce at room temperature and serve with cake.