Heat 1 tablespoon olive oil in a medium saucepan over medium heat until just hot. Add onions and garlic and cook, stirring occasionally, until just softened, about 2 minutes. Add bell pepper and mushrooms and cook, stirring occasionally, until mushrooms brown, about 3 minutes. Add rice and enough boiling water to cover by about 1/2 inch. Turn heat to low and cook, covered, until rice is half done, about 15 minutes.
In the meantime, remove grape leaves from jar. Carefully separate leaves and rinse under luke-warm water. Set each into colander to drain as you go. It's okay if the leaves overlap, even in several layers.
When rice is half cooked, take off heat and drain through a sieve to remove excess water. Place mixture back in pot and mix in the rest of the ingredients under Stuffing (Lemon Zest through Salt). Set aside to cool.
When rice is cool enough to be handled, place mixture a spoonful or two at time at the bottom of a grape leaf. Fold sides of leaf in and roll up like a tiny burrito. Fold in any section of leaf that are sticking out as you roll. The amount of rice each leaf can hold depends on how large the leaf is. In the jars I buy, the size of leaves can vary wildly. The small leaves may take only a 1/2 tablespoon and the large leaves may take up to 2 tablespoons. When in doubt, use less so you don't tear the leaves or have stuffed leaves unrolling on you.
Tear off a sheet of tin-foil about an inch wider than your steamer basket. Use a sharp knife to slash a few holes across the middle. The holes should be thin, fairly short, and number no more than 6 or 7. Place the stuffed leaves in single row in the middle of the foil lined up along the long sides. Picture a layer in a box of matches, except with stuffed grape leaves. Leave about 2 inches clear on each side of the row. Fold the sides of the foil over the stuffed leaves on either side. Fold the bottom up over the leaves. Now fold the top over as well. If there is still excess foil, carefully fold it over again. The goal is to a have a pouch that's almost fully sealed except for the holes you cut. Place the pouch in your steamer basket and repeat with more foil and the remaining grape leaves until you've got them all wrapped up. It's okay if the foil pouches rest on top of each other in the basket so long as steam can get through the holes in the bottom of each.
Fill the bottom of the steamer with enough water to come within about 1/2 inch of the bottom of the basket. Add 2 or 3 cups of white wine to the water. Bring to a boil, turn down to a simmer, cover and steam for 45 minutes.
About 15 minutes before the stuffed leaves are done, start making the dressing.
Melt the butter in a small sauce pan over medium-low heat. Add 1/2 cup white wine and heavy cream and mix well. Bring to a low simmer and cook for about 5 minutes, stirring often. Do not let the mixture boil! Add cheese and stir until melted and mixed throughly. Add 2 tablespoons white wine, salt, and pepper. Remove from heat and stir in olive oil. Set aside.
When stuffed leaves are done, remove carefully from foil pouches and divide evenly among 4 wide, shallow bowls. Reheat dressing if it cooled too much for your liking and drizzle over leaves. Serve immediately.