Working in batches, melt 2 tablespoons butter in a large skillet over medium-high heat.
Add 1/3 of the mushrooms and saute until golden brown, then season with salt and pepper to taste.
Continue with the remaining mushrooms; set aside for later.
Bring 8 cups chicken broth to a boil, then immediately reduce to a slow simmer; keep warm.
In the same skillet, melt remaining butter with olive oil over medium heat.
Saute leek just until tender, about 5 minutes.
Add rice and continue sautéing until the edges of the rice begin to look translucent.
Stir in white wine and continue cooking and stirring for about 1 minute.
Stir in 1 cup of warm chicken broth and stir occasionally until the liquid is almost absorbed.
Continue adding broth, 1 cup at a time and stirring until liquid is absorbed, all broth has been used and rice is tender and creamy.
Remove from heat and stir in cream until combined, then fold in sautéed mushrooms.
Stir in truffle oil, parmesan and chives, then taste for seasoning. Adjust seasoning with salt and pepper to taste.