For the Base:
10 ounces graham cracker crumbs
1 1/2 sticks (6 ounces) unsalted butter, melted
For the Marshmallow Layer:
4 teaspoons gelatin
1/2 cup water, divided
1/2 cup light corn syrup (OR LYLE'S GOLDEN SYRUP), divided
1 cup plus 2 tablespoons sugar
1 teaspoon pure vanilla extract
For the Chocolate Topping:
4 ounces bittersweet chocolate CHIPS
1/2 cup heavy cream
1. In large bowl, stir graham crumbs and butter together. Press firmly into bottom of 9- by 13-inch pan lined with nonstick foil. Place 1/4 cup water in small bowl and sprinkle gelatin over top. Let sit at least 5 minutes to soften.
2. Place 1/4 cup corn syrup in standing mixer bowl. Stir remaining 1/4 cup corn syrup, remaining 1/4 cup water, and sugar in medium saucepan over medium-high heat until dissolved. Continue to cook, without stirring, until mixture registers 240°F on an instant read thermometer.
3. Immediately pour hot syrup into mixer bowl and add softened gelatin and vanilla. Turn mixer to medium speed and beat until combined, about 1 minute. Increase speed to medium high and beat until light and fluffy, about 8 minutes. At this point, I added a heaping tablespoon of salted caramel. This is optional but if interested, click here for the caramel recipe.
4. Pour marshmallow over graham cracker base and smooth top with offset spatula. Chill until set, about 30 minutes.
5. Place chocolate in medium bowl. In small saucepan, heat cream until simmering and pour over chocolate and whisk until melted and smooth. Pour over marshmallow and chill until chocolate is set, about 15 minutes. Cut into squares.