Melt butter in heavy large skillet over
Add mushrooms and sprinkle with salt.
Sauté mushrooms until tender and
beginning to brown, 3 to 4 minutes.
Transfer mushrooms to medium bowl.
Bring the veg broth to simmer in medium
saucepan; keep warm.
Melt remaining tablespoons butter with
olive oil in heavy large saucepan over medium-low heat.
Add leek, sprinkle with salt, and sauté
until tender, 4 to 5 minutes.
Add rice and increase heat to medium.
Stir until edges of rice begin to look
translucent, 3 to 4 minutes.
Add white wine and stir until liquid is
absorbed, about 1 minute.
Add cup warm veg broth broth; stir
until almost all broth is absorbed, about 1 minute.
Continue adding broth by stirring until
almost all broth is absorbed before adding more, until rice is
halfway cooked, about 10 minutes.
Stir in sautéed mushrooms.
Continue adding broth, stirring until
almost all broth is absorbed before adding more, until rice is tender
but still firm to bite and risotto is creamy, about 10 minutes.
Stir in grated Parmesan cheese, if
Transfer risotto to serving bowl.
Pass additional Parmesan cheese
alongside, if desired.
Garnish with cheese tuile.