Gather all ingredients before starting the recipe.
Pre heat oven to 400°F
Butter a medium casserole dish large enough to hold the vegetables. Sprinkle with a little panko crumb to coat the bottom and the sides.
Melt 1 tablespoon of butter on high in a microwave combine melted butter with 2-3 tablespoons of panko. Stir to combine and set aside.
Chop 1/2 head Savoy cabbage into large dice and break 1/2 head cauliflower into florets.
Add vegetables to a medium sized stock pot and add enough water to cover and season with kosher salt. Bring water to a boil and cook vegetables for 2-3 minutes.
Strain liquid into a mixing bowl and reserve vegetables. Reserve 1 1/2 cups cooking liquid and discard the rest.
Using the same pot, melt 2 tablespoons of butter over medium heat and add 3 tbsp all-purpose flour. Stir to combine and cook for 2-3 minutes. Then, add 1 1/2 cups cooking liquid into roux and whisk with a wire whisk to get rid of any lumps. Add 1/2 cup milk and allow to cook until the sauce is thickened, 4-5 minutes. Remove from heat and allow it to cool slightly.
Separate 4 whole eggs, reserving the yolks separate from the whites.
Using a hand mixer, whip egg whites until they form stiff peaks.
When the sauce has cooled but is still warm, add egg yolks and stir yolks into the sauce. Return vegetables to the stock pot and stir to combine.
Gently fold whipped egg whites into vegetable mixture, season again with kosher salt and freshly ground black pepper and turn the vegetables into your casserole dish. Sprinkle the butter/ panko mixture evenly over the top of the vegetables.
Place in a 400°F pre heated oven and bake for 45 minutes, or until the top is nicely golden,
