Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius).
In a small saucepan over medium heat, melt 1/2 cup butter. Add heavy cream, brown sugar, salt, and chopped pistachios. Stir until the mixture comes to a boil, ensuring all sugar dissolves (1-2 minutes).
Turn off the heat once the mixture boils, and continue stirring until it stops bubbling.
Pour the caramel mixture into the bottom of your baking dish.
Slice the Hawaiian sweet rolls down the center without cutting all the way through and set them aside.
In a separate bowl, combine ricotta cheese, powdered sugar, and vanilla extract until well mixed.
Spread the ricotta mixture inside the sliced sweet rolls.
Place the filled rolls face down into the caramel mixture in the baking dish.
Bake for 8-10 minutes or until the rolls turn golden brown.
Remove from the oven and let them rest for about 5 minutes (avoid waiting longer).
Carefully invert the rolls onto a large serving platter placed over the baking dish.
Be cautious as the caramel is still hot. Enjoy your warm and delicious Sticky Buns!