Spread a generous dollop of peanut butter onto one side of 8 of the cracker squares, and then spread the chocolate-hazelnut spread onto one side of the other 8 squares.
Thread the marshmallows onto 2 metal skewers and carefully toast over a flame on the stove top. Place 1 toasted marshmallow onto each of the peanut-butter-covered graham crackers. Top with the chocolate-covered crackers and sandwich together gently.
Melt the white almond bark and milk chocolate in separate glass bowls set over simmering water. Set aside to cool, stirring occasionally to keep the chocolate melted.
When the toppings are at room temperature, one by one dip half of the sandwiches in the white chocolate, allowing any excess to drip off. Work quickly, and then add on whatever sprinkles or toppings you'd like to use. Repeat with the remaining 4 sandwiches, dipping them in the milk chocolate and finishing with the desired toppings.
Place in the fridge for at least 30 minutes. Then you can store the s'mores at room temperature or in the fridge until you're ready to serve!