Heat oven to 350 degrees F.
Combine the graham cracker crumbs, sugar, salt and melted butter in a small bowl until the dry ingredients are evenly moistened. Transfer the crumb mixture to a 13 x 9 x 2-inch baking pan; press crumb mixture evenly over the bottom of the pan, pressing the crumbs evenly into the corners and along the sides of the pan. Refrigerate the crust until chilled and set.
Combine the bittersweet chocolate and butter in a microwave-safe glass bowl or glass measuring cup. Heat chocolate mixture in a microwave oven on high until the chocolate and butter are melted, about 1 minute. Stir the chocolate mixture until smooth. If necessary, microwave another 15 seconds to melt.
With a hand-held electric mixer on medium-high speed, beat together the eggs and sugar in a large bowl until well blended. Reduce the speed to medium. While continuing to beat, gradually add the melted chocolate-butter mixture to the egg mixture; beat until the mixture is smooth, scraping down the side of the bowl occasionally.
Stir the flour and salt into the egg mixture. Then stir in the vanilla until smooth. Scrape the brownie mixture into the crust-lined baking pan; smooth the top level with a rubber spatula.
Bake in 350 degrees F oven for 30 minutes or until the top is smooth and the center is set when gently pressed with fingertip.
While the brownie layer is baking, whisk together the marshmallow cream and the milk in a small bowl until the mixture is well blended and smooth.
Pour the marshmallow topping mixture over the brownie layer in the pan. Spread or tilt the pan to level the topping and cover the brownie layer completely.
Sprinkle the mini chocolate kisses evenly over the marshmallow topping. Then scatter the crumbled graham crackers all over the top. Bake in 350 degrees F oven for 3 minutes or until the chocolate kisses are glossy and the marshmallow topping is set. Let cool in the pan on a wire rack. Cut into 24 bars.