- 2 pounds green beans, ends removed, halved
- 6 oz. cremini mushrooms, sliced
- 1 large yellow onion, sliced
- 1 egg, lightly beaten
- 1 cup crème fraiche (or heavy cream)
- 1 cup Parmesan cheese, grated
- 3 tablespoons butter, divided
- 1/4 teaspoon nutmeg
- kosher salt and freshly ground pepper, to taste
- Preheat oven to 375º F and bring a pot of water up to a boil.
- Heat 1 tablespoon butter in a large pan over medium-low heat. Once melted, add onion slices and saute until soft and golden, stirring frequently. 20-25 minutes. Reduce heat further if onions are getting crispy. Set aside.
- In a separate pan, heat remaining butter over high heat and add mushrooms. Cook for 3 minutes, stirring frequently, until mushrooms are slightly browned. Season with salt and pepper and set aside.
- Blanch green beans in boiling water for 5 minutes. Remove and immediately set in an ice bath to stop them from cooking more.
- Beat the egg into the crème fraiche and stir in Parmesan, nutmeg and pinch of salt and pepper.
- Add mushrooms and green beans (patted dry with a paper towel) to the crème fraiche and toss to coat thoroughly.
- Pour mixture into casserole dish (9×13-inch) and set caramelized onions around the edge as a border. Bake for 30 minutes, or until onions are slightly crisped.
- Remove from oven, let cool 5 minutes and serve hot.