Cook the pancetta in a large skillet over medium heat until the pieces turn golden and crisp. Remove the pancetta with a slotted spoon and set it aside, leaving the rendered fat in the pan.
Add the olive oil and onion to the same skillet. Cook until the onion softens, then stir in the black garlic and cook for one minute more.
Add the Arborio rice and stir to coat the grains with the fat. Pour in the white wine and cook, stirring, until the liquid mostly disappears.
Ladle in the warm broth one cup at a time, stirring often and waiting until each addition is absorbed before adding the next. Continue until the rice is tender but still has a slight bite.
Stir in the pumpkin puree and sage. Cook for two more minutes, then remove the pan from the heat. Add the butter and Parmesan cheese and stir until melted and creamy. Season with salt and pepper.
Spoon the risotto into bowls and scatter the reserved crispy pancetta over the top.