Chocolate Eclair Cake

1 1/4 cup sugar
6 tablespoons cornstarch
1 teaspoon salt
5 cups whole milk
4 tablespoons unsalted butter, cut into 4 pieces
5 teaspoons vanilla
2 tablespoons water

1 1/4 teaspoons unflavored gelatin
2 3/4 cups heavy cream, chilled
14 ounces graham crackers
1 cup semisweet chocolate chips

5 tablespoons light corn syrup

Combine sugar, cornstarch, and salt in a large saucepan. Whisk milk into sugar mixture until smooth and bring to a boil, scraping bottom with rubber spatula, over medium high heat. Immediately reduce heat to medium low and cook, continuing to scrape bottom, until thickened and large bubbles appear on surface, 4 to 6 minutes. Off heat, whisk in butter and vanilla. Transfer pudding to large bowl and place plastic wrap directly on surface of pudding. Refrigerate until cool, about 2 hours.

Stir water and gelatin together in bowl and let sit until gelatin softens, about 5 minutes. Microwave until mixture is bubbling around the edges and gelatin dissolves, 15 to 30 seconds. Using stand mixture fitted with whisk, whip 2 cups cream on medium low speed until foamy, about 1 minute. Increase speed to high and whip until soft peaks form, about 2 minutes. Add gelatin mixture and whip until soft peaks, about 1 minute.

Whisk one third whipped cream whipped cream into chilled pudding, then gently fold in remaining whipped cream, 1 scoop at a time, until combined. Cover bottom of 13x9-inch baking dish with layer of graham crackers, breaking crackers as necessary to line the bottom of the pan. Top with half of pudding whipped cream mixture and another layer of graham crackers. Repeat with remaining pudding-whipped cream mixture and remaining graham crackers.

Microwave chocolate chips, remaining 3/4 cup cream, and corn syrup in a bowl, stirring occasionally, until smooth, 1 to 2 minutes. Cool glaze to room temperature, about 10 minutes.  Cover graham crackers with glaze and refrigerate cake for 6 to 24 hours. Serve.