Inspired by the royal wedding of Prince William and Kate. This is our version of the no bake cake that was a favorite of the young prince when he visited the queen for tea.
In a medium bowl break the biscuits into almond-sized pieces and set aside.
In another medium bowl combine chocolate and butter and place on top of a saucepan with 1 inch of simmering water. Stir mixture occasionally until melted and smooth, about 3 minutes. Remove bowl from saucepan; set aside.
In a third bowl, whisk together egg, sugar, and vanilla. Place over the pan of simmering water and whisk until pale, fluffy, and thick, about 3 to 4 minutes. Remove from heat and whisk in the melted chocolate. Let cool for 5 minutes, stirring occasionally.
Fold biscuit pieces into the egg and chocolate mixture and pour into prepared pan. Chill the cake in the refrigerator for at least three hours.
When the cake is chilled, prepare the glaze. Place the cream in a saucepan over medium heat. Just as it reaches a boil, remove it from the heat and add the chocolate, stirring until completely melted and smooth.
Carefully remove the sides from the spring form pan. Invert the cake onto a wire rack, then remove the bottom of the pan from the cake. Set the rack over parchment paper to catch drips. Pour the glaze evenly over the cake, allowing it to drip down and completely cover the top and sides. Allow to firm up, then transfer to a cake plate. Slice and serve.