In large pot over high heat, bring lightly salted water to boil. Add dry egg noodles to boiling water and cook approximately 7 minutes or until al dente. Remove pot from heat, drain water, and set noodles aside.
While noodles boil, melt butter in large heavy skillet over medium heat. Once melted, add chopped onion and cook, stirring frequently, until onions soften.
Raise heat under skillet to medium-high. Add sliced mushrooms and garlic cloves. Cook, stirring occasionally, until mushrooms are limp and browned. Transfer mushrooms and onions to medium bowl and set aside.
Pour white wine into skillet to deglaze, scraping up any browned bits on bottom of skillet. Bring liquid to boil then lower heat to simmer and let liquid reduce by 50%.
Once white wine has reduced, pour in vegetable broth. Bring liquid to boil again, then lower heat to simmer. Cook until mixture has reduced by 33%. In small bowl, stir together sour cream and flour, mixing well to eliminate any lumps or clumps of flour. Reduce heat to low and return mushrooms and onions to skillet. Remove skillet from heat to stir in sour cream mixture.
Return skillet to burner. Continue cooking mixture over low heat until sauce thickens. Stir in parsley and season with salt and pepper to taste. Portion egg noodles into serving bowls and top with mushroom mixture. Serve warm.