9 lasagna noodles
1 (15-ounce) package whole milk ricotta
2 (10-ounce) packages frozen chopped spinach, thawed and drained
3 cups shredded mozzarella cheese, divided
3/4 cup freshly grated Parmesan, divided
2 tablespoons chopped fresh parsley leaves
1/4 cup unsalted butter
2 cloves garlic, minced
1 pound cremini mushrooms, thinly sliced
1 onion, diced
1/4 cup all-purpose flour
3 cups milk, at room temperature
1 teaspoon dried basil
1/2 teaspoon dried oregano
Pinch of nutmeg
Kosher salt and freshly ground black pepper, to taste