Heat oven to 375 degrees F.
Toss 1/4 cup walnuts with about 1 teaspoon powdered sugar.
Place on baking sheet.
Bake 6 to 8 minutes, stirring occasionally.
Watch carefully to avoid burning.
Whisk together remaining walnuts, oil, stock, vinegar, garlic and shallots to form dressing.
Season with salt and pepper.
Combine spinach, mushrooms and bacon in large bowl; add dressing.
Toss to coat.
Divide onto serving plates.
Sprinkle with toasted walnuts and blue cheese.