In a large mixing bowl, whisk together both instant vanilla pudding mixes, evaporated milk, and milk until well combined and thickened. Set aside.
In a separate mixing bowl, beat 1 cup heavy cream, powdered sugar, and vanilla extract together until stiff peaks form.
Gently fold the freshly whipped cream into the prepared pudding mixture until fully combined.
In a 13"x9" baking dish, arrange a single layer of graham crackers on the bottom. You may need to break some crackers to fit them in evenly.
Spoon half of the pudding mixture over the layer of graham crackers and spread it out evenly with a spatula.
Add another layer of graham crackers on top of the pudding mixture, followed by the remaining pudding cream mixture. Smooth it out with a spoon or spatula.
Pour chocolate chips into a small bowl. In a small saucepan, heat heavy cream over medium heat until it begins to simmer. Remove from heat and pour over the chocolate chips. Let it sit for a minute, then stir until the chocolate is completely melted and the mixture is smooth.
Pour the chocolate ganache over the top layer of the eclair cake, spreading it out evenly with a spatula.
Cover the baking dish with plastic wrap and refrigerate for at least 4 hours, or overnight, to allow the pudding mixture to set and the flavors to meld together.
Slice the eclair cake into squares and serve cold.