Heat 2 tablespoons oil in heavy large saucepan over medium heat. Add onion; sauté 5 minutes. Add wine, beef broth, thyme and 1 bay leaf; boil until liquid is reduced to 1 cup, about 35 minutes. Strain sauce into small saucepan.
Preheat oven to 350°F Place orzo on rimmed baking sheet. Bake until golden brown, about 20 minutes.
Heat 2 tablespoons oil in another heavy large saucepan over medium-high heat. Add shallots; sauté 4 minutes. Add mushrooms; sauté until golden, about 10 minutes. Add orzo, chicken broth and 1 bay leaf; bring to boil. Reduce heat to medium-low. Cook uncovered until orzo is tender and broth is absorbed, stirring often, about 20 minutes. Add cream and tarragon; simmer 5 minutes, stirring occasionally. Season with salt and pepper.
Heat 3 tablespoons oil in heavy large nonstick skillet over medium-high heat. Sprinkle salmon with salt and pepper. Add to skillet and sauté just until cooked through, about 3 minutes per side.
Bring sauce to simmer. Add butter; whisk just until melted. Season with pepper. Spoon orzo onto plates. Top with salmon. Serve with sauce.