S'mores Bars Recipe

Ingredients

• 3 cups graham cracker crumbs (about 20 graham crackers)
• 2 sticks unsalted butter (16 Tbsp.), melted
• ½ tsp. kosher salt
• 1 ½ sticks unsalted butter (12 Tbsp.)
• ¼ cup unsweetened cocoa powder
• 1 Tbsp. instant espresso powder
• 2 cups sugar
• ¾ cup buttermilk
• 2 eggs
• 2 Tbsp. pure vanilla extract
• 2 ¼ cups all-purpose flour
• 1 tsp. baking soda
• 1 bag milk chocolate chips (11.5 oz.), such as Ghirardelli
• 3 egg whites
• ¼ tsp. cream of tartar
• 1 jar marshmallow creme (7 oz.)