01 - Preheat oven to 375°F (190°C).
02 - Bring a large pot of salted water to a boil. Add green beans and blanch for 2–3 minutes until bright green and slightly tender. Drain and rinse with cold water. Set aside.
03 - In a large skillet, melt butter over medium heat. Add garlic, onion, and mushrooms (if using), sautéing for 5 minutes until softened.
04 - Stir in flour and cook for 1 minute. Gradually whisk in vegetable broth and milk, cooking until thickened, about 3–5 minutes.
05 - Stir in Parmesan cheese, salt, and pepper. Remove from heat.
06 - Add the green beans to the sauce and toss to coat evenly.
07 - Transfer the mixture to a greased 9×9-inch or similar-sized baking dish.
08 - Sprinkle toasted almonds evenly over the top.
09 - Bake uncovered for 20–25 minutes until bubbly and lightly golden.