For chocolate custard

1. Pour half and half into a medium saucepan over medium-low heat. In a medium glass bowl, whisk together sugar, egg yolks, cornstarch and salt until thick and creamy, about 2 minutes.
2. When half & half begins to steam, pour a thin stream into the sugar and egg mixture. Whisk constantly to temper the egg yolks.
3. Continue to whisk until smooth before pouring the mixture back into the saucepan. Add the chopped chocolate and espresso powder. Whisk to combine.
4. Stirring constantly, cook the custard over medium-low heat until the mixture is thick enough to hold the outline of a figure 8 made with the backside of a spoon. Remove the custard from heat and immediately whisk in the butter and vanilla extract.
5. Pour the custard into a clean glass bowl and cover the bowl with plastic wrap. Cool to room temperature.
6. When the custard reaches room temperature, beat the heavy cream and confectioners sugar on medium high speed with a hand mixer until it forms medium peaks.
7. Use a large spatula to gently fold the whipped cream into the cooled custard. Set aside.

For vanilla whipped cream layer

1. In a medium bowl, use a hand held mixer to whip the heavy cream, confectioners sugar and vanilla until stiff peaks form. Set aside.

To assemble the icebox cake

1. Line a 9 x 5 inch loaf pan with plastic wrap on all sides. Be sure to cover the bottom and sides of the pan, allowing the plastic wrap to hang over the sides of the pan by about 6 inches to wrap the top of the cake once assembled.
2. Place a layer of graham crackers on the bottom of the pan, cutting the crackers as needed to fit them in an even layer.
3. Top with a layer of chocolate custard (about 1 1/2 cups). Spread evenly with an offset spatula.
4. Add a layer of vanilla whipped cream, again spreading with a clean offset spatula.
5. Repeat the process of layering the graham crackers, chocolate custard and vanilla whipped cream one more time. Top with a final layer of custard and finish with a layer of graham crackers.
6. Use the excess plastic wrap to cover the top of the icebox cake. Refrigerate for at least 12 hours.
7. When ready to serve the cake, make the mocha whipped cream by beating together the heavy cream, confectioners sugar, vanilla and espresso on high speed until thickened and spreadable.
8. Carefully unwrap the cake and invert the pan onto a serving platter or cutting board.
9. Remove the pan along with the plastic wrap. Use an off set spatula or knife to cover the cake on the top and sides with the mocha whipped cream. Sprinkle the top with chopped chocolate if desired.
10. Cake should be chilled before slicing. For best results, use a large, sharp knife to slice the cake. Wash the knife with warm water and dry it completely in between slices.