1/4 cup (1/2 stick) unsalted butter, cut into pieces
3/4 cup sour cream
2 large eggs, beaten
1 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
1/4 cup finely grated parmesan cheese
Instructions
Preheat oven to 400°F and grease 8-inch square baking pan.
Cook macaroni according to package instructions in a large pot of salted boiling water; add chopped broccoli 3 minutes before pasta is finished cooking; drain well. Use a blender to combine milk and spinach.
While pasta is hot, stir in all but 1/2 cup of the cheddar, butter, sour cream, milk + spinach, eggs, salt, and pepper.
Scrape the mixture into the prepared pan. Sprinkle the remaining cheddar and the parmesan over the top. Bake until the casserole is firm to the touch and golden, green-ish brown, about 30 minutes.