01 - Preheat oven to 375°F. Lightly grease four individual ramekins or a medium baking dish with cooking spray or butter.
02 - Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1 minute, stirring constantly. Gradually whisk in milk, continuing to stir until sauce thickens. Add Gruyère cheese, nutmeg, salt, and pepper. Remove from heat once smooth and creamy.
03 - Heat a skillet over medium-high heat. Add spinach and sauté briefly until just wilted, about 1-2 minutes. Remove from heat and set aside.
04 - Place puff pastry or toasted brioche at the bottom of each ramekin. Layer with sautéed spinach, zucchini slices, tomato, and ham or mushrooms.
05 - Spoon the prepared cheese sauce evenly over the layered ingredients in each ramekin.
06 - Create a shallow well in the center of each ramekin. Crack one egg into each well. Season eggs lightly with salt and pepper.
07 - Bake for 20-25 minutes until egg whites are set but yolks remain runny. Adjust cooking time for firmer yolks if desired.
08 - Remove from oven. Garnish with chopped fresh chives or parsley. Serve immediately while warm.