Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment paper.
Layer bottom of the baking sheet with graham cracker crumbs.
Melt butter in a saucepan over medium heat. Add sugar; cook and stir until dissolved, about 2 minutes. Bring to a boil; cook until a thickened caramel is formed, about 1 minute more. Pour quickly onto the crackers; spread with a spatula. Sprinkle almonds on top.
Bake in the preheated oven until bubbling and golden brown, 8 to 10 minutes. Turn oven off; open door slightly and let the brittle cool in the oven for 1 hour. Sprinkle salt on top; cool until set, about 1 hour more. Crack into pieces by hand.