Peel, core, and dice the pear. Set half of the diced pear aside.
Place the other half of the diced pear in a small saucepan with a little water, and cover. Bring the water to a simmer and cook over medium-low heat for 5-15 minutes until tender. (The time will vary depending on the ripeness and type of pear chosen. Add a little more water if needed.)
Puree the cooked pear using a food processor or blender or by mashing with a fork. Set aside.
Heat the broth in a saucepan until it comes to a simmer. Cover and reduce the heat to low to keep the broth at a low simmer throughout the risotto-making process.
Meanwhile, add the oil to a large saucepan and place over medium heat. Once hot, add the onion and saute for 5-6 minutes until translucent.
Add the rice and stir to evenly coat in oil. Toast for 2-4 minutes, stirring frequently.
Pour in the wine and cook it until it evaporates, stirring frequently, about 1-2 minutes.
Add 2 ladlefuls of hot broth, or enough to barely cover the rice, and stir well. Let the rice cook, stirring frequently and keeping the heat at a simmer, until the broth is absorbed.
Continue to add broth 1 ladleful at time and let it absorb, stirring all the while. Do this until the rice is cooked but still al dente, about 15-18 minutes. (You may not use all of the broth.)
Remove the pan from heat and stir in the pureed pear, butter, and Parmesan.
Divide risotto among wide, shallow bowls, garnish with the remaining diced pear, and drizzle the balsamic vinegar on top. Serve immediately.