01 -
Heat the oven to 400°F (200°C). Line a 10x15-inch or similar rimmed baking sheet with parchment paper, then arrange the graham crackers in a tight single layer.
02 -
Melt the butter, brown sugar, and fine salt in a saucepan over medium heat. Bring to a strong boil and cook for 3 minutes without stirring, then remove from the heat and stir in the vanilla.
03 -
Pour the hot toffee over the graham crackers and spread it gently with a spatula. Bake for 5-6 minutes, until the surface is bubbling all over.
04 -
Remove the pan from the oven and scatter the chocolate evenly over the hot toffee. Return to the oven for 1 minute, then spread the softened chocolate into an even layer.
05 -
Sprinkle mini marshmallows and crushed graham crackers over the chocolate. Broil for 30-60 seconds, watching constantly, just until the marshmallows puff and lightly brown.
06 -
Cool at room temperature for 10 minutes, then refrigerate for 30 minutes or until firm. Score into squares or break into pieces before serving.