• Heat the oven to 425° with a rack set to the middle of the oven.

For the breadcrumb topping

• Mix the breadcrumbs in a bowl with 1/2 teaspoon kosher salt, 1 teaspoon minced garlic, and 1/4 cup parmesan cheese.

  Drizzle with 1 Tablespoon olive oil and stir until the mixture is combined completely and set aside.
  1/2 cup fresh breadcrumbs, 3 teaspoons kosher salt, 3 teaspoons minced garlic, 2 T olive oil

For the mushrooms

• Add 1 Tablespoon olive oil and 1 Tablespoon of butter to a large 10" skillet or enameled cast iron pan over medium high heat. Once the butter has melted, sauté the mushrooms with a generous 1 teaspoon sprinkle of salt. Cover the pan and let them release all their water.
  6 Tablespoons unsalted butter, 1 lb baby portobello mushrooms
• After about 8 minutes, remove the lid to let the water cook off and let them brown completely another 7 minutes or so. Right before they’re finished cooking at about the 5-6 minute mark, add another tablespoon of butter along with the shallots, remaining 2 teaspoons garlic and thyme and finish cooking. Remove to a plate.
  1 shallot, 1 teaspoon chopped fresh thyme

For the sauce

• To same pan, add the remaining butter (4 T) and cook with the flour to make a roux. Stir for two minutes. Add in the milk (and cream if using) and cook until thickened and the sauce coats the back of a spoon. Season with remaining 1 1/2 teaspoons of salt, 1/2 teaspoon of black pepper and stir in the remaining parmesan cheese (1/2 cup)
  4 TBSP all purpose flour, 4 cups 2% milk, 1/2 teaspoon black pepper
• Stir in the chicken, sun dried tomatoes, handfuls of baby spinach and finally the cooked pasta tossing in the sauce until evenly coated.
  2 cooked chicken breasts, 2 cups fresh spinach leaves, 6-8 sun dried tomatoes, 1 lb cooked rigatoni pasta
• Evenly sprinkle the breadcrumb mixture over the whole pan and bake for about 15 minutes until the top is golden.