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 to form a roux. Gradually whisk in milk, stirring constantly until sauce thickens. Remove from heat and stir in Gruyère cheese, nutmeg, salt, and pepper until smooth.
03 - Heat a skillet over medium-high heat. Add spinach and sauté briefly until just wilted, about 2-3 minutes. Remove from heat and set aside.
04 - Place one slice of puff pastry or toasted brioche in the bottom of each ramekin. Layer with sautéed spinach, zucchini slices, tomato, and ham (or mushrooms for vegetarian version). Repeat for all four ramekins.
05 - Spoon cheese sauce evenly over the layered ingredients in each ramekin. Create a shallow well in the center of each and carefully crack one egg into each well. Lightly season eggs with salt and pepper.
06 - Bake for 20-25 minutes until egg whites are set but yolks remain runny. For firmer yolks, extend baking time by 3-5 minutes. The edges should be golden and bubbly.
07 - Remove from oven and let rest for 2 minutes. Sprinkle with fresh chives or parsley. Serve immediately while hot, accompanied by a crisp green salad if desired.