Bring a pot of water to a boil, add 1 Tsp salt, and add the Green Beans. Boil for 2-3 minutes to blanch the Green beans. Then strain and set aside to cool.

Caramelize the onions by heating a pot over medium low heat. To it add butter, and the sliced onions and stir them until the onions wilt and turn a brown color.

Create the white sauce by heating a sauce pan over medium heat. To it add butter, and all purpose flour to create a roux. Then add the milk slowly to prevent lumps. Then add the salt, black pepper, cayenne pepper, thyme and nutmeg.

In a small bowl, add the Panko breadcrumbs and drizzle in 2 Tbsp of melted butter. Gently mix until all the breadcrumbs have absorbed the butter.

Preheat the oven to 375 F (or 190 C)

Grease a 9" x 13" casserole dish. Add half of the French Onions and spread them out evenly. Then add half of the Green Beans, and spread them evenly. Then ladle on half of the white sauce. Then add a layer of shredded Gruyere cheese. Then repeat starting with the Green Beans, then white sauce, then French Onions, and then Gruyere cheese. Atop the cheese add a layer of Panko Breadcrumbs. Then add a layer of grated parmesan cheese.

Put in the oven uncovered, and bake for 25 minutes at 375 F.

After 25 minutes, remove from oven, and allow to cool for 10 minutes before serving.

Enjoy :)