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 to form a roux. Gradually add milk while whisking constantly until the sauce thickens. Stir in 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 2 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 in each dish.
05 - Spoon the prepared cheese sauce evenly over the layered vegetables and ham in each ramekin.
06 - Create a shallow well in the center of each ramekin using the back of a spoon. Crack one egg into each well. Lightly season the eggs with salt and pepper.
07 - Transfer the ramekins to the preheated oven. Bake for 20 to 25 minutes until the egg whites are fully set but the yolks remain runny. Adjust baking time by 2-3 minutes for firmer yolks if desired.
08 - Remove from the oven. Sprinkle with chopped fresh chives or parsley. Serve immediately while hot.