Melt 1 tablespoon of butter in a large pot over medium heat. Add the sage leaves and cook for 1 to 2 minutes until crisp. Remove the leaves with a slotted spoon and set them aside on a paper towel.
Add the diced onion to the same pot and cook for 3 minutes until softened. Stir in the garlic and cook for 30 seconds more.
Add the cubed butternut squash and cook for 5 minutes, stirring occasionally. Stir in the Arborio rice and cook for 1 minute to toast it lightly.
Pour in 1 cup of the warmed broth and stir until mostly absorbed. Continue adding broth 1/2 cup at a time, stirring often, until the rice is tender and creamy, about 20 minutes total.
Remove the pot from the heat. Stir in the remaining 2 tablespoons of butter, the Parmesan cheese, salt, and pepper until well combined.
Divide the risotto among bowls and top each serving with the crispy sage leaves.