Heat the chicken broth in a saucepan and keep it warm over low heat. In a large pot, melt 2 tablespoons of the butter over medium heat. Add the onion and garlic, cook until softened, then stir in the arborio rice for one minute.

Add the warm broth one ladle at a time, stirring often until each addition is absorbed. Once the rice is tender and creamy, stir in the pumpkin puree, half of the Parmesan, and salt and pepper to taste. Spread the mixture on a baking sheet to cool completely.

Once cooled, scoop the rice into 12 equal portions and roll into balls. Set up three bowls with the flour, beaten eggs, and panko breadcrumbs. Coat each ball in flour, then egg, then breadcrumbs.

Heat vegetable oil in a deep pot to 350°F. Fry the arancini in batches until golden brown on all sides, about 3 to 4 minutes per batch. Drain on paper towels.

In a skillet, melt the remaining 2 tablespoons of butter over medium heat. Add the sage leaves and cook until the butter turns golden brown and the leaves crisp. Remove from heat.

Arrange the arancini on a serving plate, drizzle with the sage brown butter, scatter the crisp sage leaves over top, and finish with the remaining Parmesan.