Line a baking sheet with parchment paper if desired.
Break 8 graham crackers in half crosswise so you have 16 pieces.
Place on the baking sheet and top 8 of the pieces with 1 large marshmallow each.
Option 1: For deep golden-brown marshmallows: Arrange a rack in the middle of the oven and heat the oven to 450ºF. Bake the marshmallows and graham crackers until the marshmallows are deep golden-brown on top, about 5 minutes.
Option 2: For charred marshmallows: Arrange a rack in the upper third of the oven and heat the oven to broil. Broil the marshmallows and graham crackers until the marshmallows are slightly charred on top, about 2 minutes.
Remove the baking sheet from the oven.
Divide 2 ounces chocolate bar over the marshmallows and sprinkle with flaky salt if desired.
Close the s’mores by topping with the remaining graham crackers.
Let sit 5 minutes for the chocolate to melt and for the marshmallows to cool slightly before serving.
