Sweat (cook without browning) in a saucepan over medium heat with 2 tablespoons butter, stirring occasionally, until softened.
Add mushroom and sauté until moisture evaporates
Add rice, stirring to coat with butter.
Deglaze with white wine and reduce by ½.
Add 1 cup simmering broth mixture and cook, stirring constantly and keeping at a simmer, until absorbed.
Continue cooking at a simmer and adding broth mixture, about 1/2 cup at a time, stirring constantly and letting each addition be absorbed before adding next, until rice is tender and creamy-looking but still al dente, about 18 minutes total. (There may be broth left over.)
Remove pan from heat.
Stir in Parmesan and remaining 3 tablespoons butter, and salt and pepper to taste.