Pastry Cream (note, pastry cream will take at least 90 minutes to cool before it can be used. This cream can be prepared up to 2 days in advance of using and stored in an airtight container in the refrigerator until ready to use).

In a medium-sized saucepan, whisk together sugar, cornstarch, and salt.

In a separate bowl or large measuring cup, whisk together milk, cream, and egg yolks until completely combined.

Return to the cornstarch mixture, and, while whisking it, slowly drizzle in the milk/cream/egg yolk mixture until combined. Turn stovetop heat to medium and cook, stirring constantly, until mixture begins to thicken to a pudding-like consistency (this may take some time depending on your particular stove, but don't turn up the heat or you could cook the pastry cream too fast or even prevent it from thickening properly).

As soon as pudding has thickened and the whisk leaves trails through the surface (another good way to check if it is finished is to dip a spoon in the mixture and see if the back of the spoon is entirely coated), remove from heat and pour through a fine mesh strainer into a large heatproof bowl.

Add butter, one tablespoon at a time, whisking after each addition until melted. Stir in vanilla extract. Mixture should be smooth.

Allow pastry cream to cool for 15 minutes, stirring occasionally, then press a piece of wax paper or plastic wrap directly against the surface of the pastry cream (to prevent a skin from forming) and transfer to the refrigerator to cool until completely chilled (about 90 minutes). One pastry cream is chilled, you can make your whipped cream and assemble your eclair cake!

Whipped Cream

Prepare whipped cream by combining cold heavy cream, powdered sugar, and vanilla extract in a large bowl and using an electric mixer to beat on high-speed until you have achieved stiff peaks (a thick fluffy mixture similar in consistency to Cool Whip).

Assembly

Fold prepared whipped cream into completely cooled pastry cream until completely combined.

Place a single layer of graham crackers into the bottom of a 13×9” (23x33cm) baking dish. Layer with half of your pastry cream/whipped cream mixture, and use a spatula to smooth so you have a flat, even layer.

Gently nestle a second layer of graham crackers onto the surface of the pastry cream. Top with remaining pastry cream and smooth again so you have an even surface.

Top the pastry cream with a final layer of graham crackers. Place the tray in the refrigerator while you prepare your ganache topping.

Chocolate Ganache

Combine finely chopped chocolate and heavy cream in a medium-sized, heat-proof bowl. Place in the microwave and heat in 30-second increments, stirring in between, until mixture is smooth and glossy.

Allow ganache to cool for several minutes then remove eclair cake from refrigerator and spread ganache evenly over the graham cracker surface.

Cover and return to refrigerator for several hours (preferably overnight) before cutting and serving.