Mushroom Panzanella

I found this on Napa Style and it is delicious! Don't let the long laundry list frighten you, they are a lot of steps that can be done ahead.

• Ready In: 55 mins
• Serves: 4-6

Ingredients

• CROUTONS

• 1  lb  loaf  crusty Italian bread, sliced in 3/4-inch pieces crusts removed
• 6  tablespoons unsalted butter
• 3  tablespoons  minced garlic
• 1  tablespoon  finely minced fresh thyme
• 1⁄2 cup  finely grated parmesan cheese
•  salt
•  freshly ground coarse black pepper

• ROASTED ONION PUREE

•  kosher salt
• 3  whole onions, peeled
• 1  cup low sodium chicken broth or 1  cup water

• MUSHROOMS

• 1⁄4 cup olive oil
• 1  lb mushroom, cleaned and thickly sliced

• TO ASSEMBLE

• 6  tablespoons olive oil, plus more for drizzling
• 3  tablespoons red wine vinegar, plus more for drizzling
• 1⁄2 cup  finely grated parmesan cheese, plus more for garnishing
• 1  tablespoon  finely mince fresh thyme
• 2  ounces  Baby Spinach or 2  ounces baby arugula
• 1⁄4 red onion, very thinly sliced
• 3⁄4 cup celery heart (sliced thinly on the diagonal, plus some more of the chopped leaves)
•  salt

Directions

1. CROUTONS:
2. Preheat oven to 300ºF.
3. Place the bread cubes in large bowl.
4. In a large skillet, heat oil and butter over moderate heat.
5. Add the garlic and sauté 1 minute, then add thyme.
6. Pour over breadcrumbs and stir immediately.
7. Add 1/4 cup of Parmesan cheese and toss well.
8. Season with salt and black pepper to taste.
9. Spread on baking sheet, sprinkle with the remaining cheese, and place in the oven for about 20 minutes, or until light brown.
10. Return them to the large bowl and set aside.
11. ROASTED ONION PURÉE:
12. Preheat oven to 450ºF.
13. Layer 1/2" of kosher salt in a shallow baking pan.
14. Place the onions in the pan and roast, turning occasionally, until golden brown and tender, about 15-18 minutes.
15. Place the roasted onions and the broth into a blender and purée; set aside.
16. MUSHROOMS:
17. In a large skillet, heat the olive oil.
18. Add the mushrooms and sauté until fully cooked and well browned.
19. TO ASSEMBLE:
20. Add the mushrooms and roasted onion purée to the croutons, and toss well to coat.
21. Add the oil, vinegar, Parmesan and thyme.
22. Mix well.
23. Arrange the spinach or arugula, onions and celery on serving platter.
24. Drizzle with red wine vinegar and oil.
25. season with salt and pepper to taste.
26. Top with crouton mixture, and garnish with additional Parmesan, as desired.