Preheat oven to 350 F. and grease and line a 9x13 baking pan with parchment paper, ensuring that the paper along the long sides extends above the pan a bit, to act as handles to remove from the pan later. Set aside.
Place the graham crackers in a large ziplock and smash them into fine crumbs using a heavy object, I used a rolling pin. It helps to place the bag on a layered hand towel to absorb the impact. Transfer crackers to a medium bowl, add butter and mix with a fork until uniform. Reserve 1 tbsp of the graham cracker crumb.
Transfer graham crackers to a 9x13 pan. Press crackers down using the back of a glass. Bake crust for 10 minutes or until smell golden. Transfer to a cooling rack until cooled. (leave oven on!)
Place marshmallows on top of the baked graham crackers, side by side leaving little to no gap in between each marshmallow.
Toast almond slivers in a pan on medium-low heat until light brown, make sure not to burn. Set aside to cool. Mix in the tbsp of crumb with almonds.
Melt chocolate in the microwave, heating in 30 second intervals and mixing thoroughly between each interval. Mix until all smooth and melted.
Top marshmallows with melted chocolate. Spread to cover marshmallow layer. Sprinkle reserved graham cracker/almond crumb all over. Bake for 10-12 minutes to allow the marshmallow to melt. Transfer to a cooling rack. Sprinkle the sea salt.
When the s’mores are cooled, transfer to the freezer for 30 minutes. Then, let them sit on the counter for about 10 minutes before cutting.
Store in an airtight container at room temperature for up to a week.
Notes
When you slice the bars, the graham cracker crust will become crumby but you should still have a solid cracker layer. You can adjust the butter amount to get a less crumbly crust as an option.