1. Prepare the Filling

1. Heat butter in a skillet over medium heat. Add diced onion and sauté until translucent, about 3–4 minutes.
2. Stir in the chopped mushrooms and cook until softened and any liquid has evaporated, about 5 minutes.
3. Sprinkle flour over the mushroom mixture and stir to coat. Cook for 1–2 minutes to remove the raw flour taste.
4. Gradually pour in the milk, stirring constantly to form a smooth mixture. Add the heavy cream and cook until the mixture thickens, about 3–4 minutes.
5. Season with salt, black pepper, and nutmeg (if using). Stir in fresh parsley for added flavor. Remove from heat and let cool slightly.

2. Chill the Mixture

• Transfer the filling to a shallow dish, spreading it evenly. Cover with plastic wrap and refrigerate for at least 1 hour or until firm enough to shape.

3. Shape the Croquettes

• Once chilled, divide the filling into 10–12 equal portions. Shape each portion into a cylinder or oval about 2 inches long. Place the shaped croquettes on a tray and refrigerate for another 15–20 minutes to firm up.

4. Coat the Croquettes

1. Prepare a breading station with three shallow bowls: one with flour, one with beaten eggs, and one with breadcrumbs.
2. Roll each croquette in flour, then dip it into the beaten eggs, and finally coat it thoroughly with breadcrumbs. Press gently to ensure the coating adheres.

5. Fry the Croquettes

1. Heat about 2 inches of oil in a deep skillet or pot to 350°F (175°C).
2. Fry the croquettes in batches, 2–3 at a time, to avoid overcrowding. Cook for 2–3 minutes per side or until golden brown and crispy.
3. Remove with a slotted spoon and drain on paper towels.

6. Serve and Enjoy

• Serve the croquettes hot, garnished with fresh parsley and grated Parmesan if desired. Pair with a dipping sauce, such as aioli or garlic cream sauce.