In a saucepan, bring broth and 2 cups water to a bare simmer over medium.
In a large saucepan, melt 1 tablespoon butter over medium. Add onion and carrots; season with salt and pepper. Cook, stirring occasionally, until softened, 5 to 7 minutes. Stir in rice. Add wine; cook, stirring, until absorbed, 1 to 2 minutes.
Add 2 cups hot broth; simmer over medium-low, stirring frequently, until mostly absorbed, 10 to 12 minutes. Continue to add broth, 1 cup at a time, stirring occasionally, until absorbed before adding more. Cook until rice is creamy and just tender, about 20 minutes (you may not need all the broth).
Remove risotto from heat. Stir in Parmesan and 1 tablespoon butter, and season with salt and pepper.