Heat chicken broth in a stockpot over medium-low heat until warmed.
Heat 1 tablespoon butter and olive oil in a large, heavy-bottomed pan; cook and stir onion in the melted butter-oil mixture until translucent, about 2 minutes. Add rice to onion mixture and stir to coat; cook and stir rice mixture until fragrant, about 1 minute.
Pour wine into rice mixture; cook and stir until liquid is absorbed, about 5 minutes. Add 1 ladle of hot chicken broth to rice mixture, stirring constantly, until broth is absorbed. Continue adding 1 ladle of broth at a time until rice is tender but firm to the bite, 20 to 30 minutes.
Mix 2 tablespoons butter, truffle oil, Parmesan cheese, and milk into risotto until fully incorporated; season with salt, pepper, and parsley.