01 - Preheat the oven to 375°F. Lightly grease four individual ramekins or one 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 the sauce thickens and bubbles. Remove from heat, stir in Gruyère cheese, nutmeg, salt, and pepper until smooth and creamy.
03 - Heat a skillet over medium-high heat. Add spinach and cook briefly until wilted, about 2 minutes. Remove from heat and drain any excess liquid.
04 - Place one slice of puff pastry or toasted brioche in the bottom of each prepared ramekin. Layer the sautéed spinach, zucchini slices, tomato, and ham or mushrooms evenly among the ramekins.
05 - Spoon the prepared cheese sauce generously over the layered vegetables and meat in each ramekin, ensuring even distribution.
06 - Create a shallow well in the center of each ramekin through the layers. Crack one egg into each well. Season the eggs lightly with additional salt and pepper.
07 - Place ramekins in the preheated oven and bake for 20 to 25 minutes, until egg whites are completely set but yolks remain slightly runny. Adjust cooking time by 2 to 3 minutes for firmer yolks if preferred.
08 - Remove from oven and immediately sprinkle with freshly chopped chives or parsley. Serve hot directly from ramekins.