Begin by melting butter in a medium bowl, mixing it with sugar and crushed graham crackers until uniform. Press this mixture firmly into the bottom of a 9x13-inch dish, creating an even layer. Chill in the refrigerator for about 15 minutes, allowing the crust to set while you prepare the creamy filling.

In a saucepan over medium heat, combine a small amount of milk with cornstarch until smooth. Gradually whisk in the remaining milk, sugar, and vanilla extract. Cook while stirring constantly for 8-10 minutes, or until the mixture thickens and bubbles. Once thick, remove from heat and stir in butter until melted and integrated, then allow the cream to cool slightly.

Spread half of the warm pastry cream evenly over the chilled graham cracker crust, ensuring full coverage. Next, layer additional graham crackers on top of the cream, creating a crunchy middle layer. Finish by spreading the remaining pastry cream on top, smoothing it out for an even surface, ready for the chocolate topping.

In a small saucepan, melt the butter over low heat. Stir in cocoa powder and cream until the mixture is smooth and glossy. Gradually add sifted powdered sugar and remaining vanilla, whisking until thick. This rich chocolate topping is now ready to be poured over the assembled layers, creating a delicious finish for your No Bake Chocolate Éclair Cake.

Cover the cake with plastic wrap, ensuring it’s airtight to prevent any drying out. Refrigerate the dessert for at least 1 hour, or preferably overnight, allowing the flavors to meld beautifully. Once chilled, the No Bake Chocolate Éclair Cake is set and ready to slice, revealing its delectable layers when served.