Remove from heat, add salt and stir until combined. Let sauce cool before using. You can keep it in the fridge for about 20 days. Warm it gently before using. But if you are going to use it in this recipe, use it while room temperature, not cold and not warm either.
With a small spoon, carve a hole on top of the cupcake, about 3/4 inch deep. Fill it with a teaspoon of the Cashew Pastry Cream. Pipe the Salted Caramel Buttercream on top. Top with caramelized cashews! Voila!