Eclair Cake with Chocolate Ganache

Preheat the oven to 400 degrees F (200 degrees C). Grease a 9x13-inch baking dish. Place a mixing bowl in the freezer to chill.

Make pastry shell: Combine water, butter, and salt in a medium saucepan and bring to a boil over medium-high heat. Reduce heat to medium and stir in flour. Cook and stir until mixture pulls away from the sides of the pan and forms a ball. Transfer mixture to a mixing bowl and beat in eggs, one at a time, until fully incorporated. Spread dough evenly in the bottom of the prepared baking dish.

Bake in the preheated oven until golden brown, 25 to 30 minutes. (The dough will rise and make a boat shape, but should drop as it cools.) Cool completely on a wire rack.

Make filling: Remove the chilled mixing bowl from the freezer and pour in cold whipping cream. Whip until cream thickens, about 1 minute. Stir in confectioners' sugar and vanilla. Continue to whip until cream forms stiff peaks. Place whipped cream in the refrigerator to keep chilled.

Pour pudding mixes and milk into a separate mixing bowl and stir until creamy. Fold in whipped cream. Spread filling over cooled crust and refrigerate.

Make ganache: Place chopped chocolate in a heat-proof bowl. Bring cream almost to a boil in a small saucepan over medium heat. Pour hot cream over chocolate; let sit for 1 minute, then whisk until smooth. Let cool until ganache is thickened, about 10 minutes.

Pour ganache over cream filling, spreading to cover the entire surface. Return the pan to the refrigerator and chill for at least 1 hour before serving.