Heat chicken broth in a stockpot over medium-low heat until warmed, 3 to 5 minutes.
Heat 1 tablespoon butter and olive oil in a large, heavy-bottomed pan until butter melts. Add onion and sauté until translucent, about 2 minutes. Stir in rice until coated, then cook, stirring constantly, until fragrant, about 1 minute.
Pour wine into rice mixture; cook and stir until liquid is absorbed, about 5 minutes. Add one ladle hot broth and cook, stirring constantly, until broth is absorbed. Continue adding and stirring in one ladle broth at a time until rice is tender but firm to the bite, 20 to 30 minutes. If you run out of broth before rice is cooked, finish cooking with hot water.
Stir in Parmesan, remaining 2 tablespoons butter, truffle oil, and milk until fully incorporated, then season with parsley, salt, and pepper. Serve immediately.