01 - Preheat the 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 until bubbly. Gradually whisk in milk, stirring constantly until sauce thickens and bubbles. Remove from heat, stir in Gruyère cheese, nutmeg, salt, and pepper until smooth.
03 - Heat a skillet over medium-high heat. Add spinach and cook briefly until wilted, about 2 minutes. Remove from pan and drain excess liquid.
04 - Place a slice of puff pastry or toasted brioche in the bottom of each ramekin. Layer with sautéed spinach, zucchini slices, tomato, and ham or mushrooms in each dish.
05 - Spoon cheese sauce evenly over the layered ingredients in each ramekin. Create a shallow well in the center of each and carefully crack an egg into each well. Lightly season eggs with salt and pepper.
06 - Transfer ramekins to the preheated oven. Bake for 20 to 25 minutes until egg whites are set but yolks remain slightly runny. Adjust baking time by 2 to 3 minutes for firmer yolks if desired.
07 - Remove from oven and let rest for 2 minutes. Sprinkle with fresh chopped chives or parsley. Serve immediately while warm.