01 - Preheat 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 pour in milk while whisking continuously to prevent lumps. Continue whisking until sauce thickens and bubbles. Remove from heat and stir in Gruyère cheese until melted. Add pinch of nutmeg, salt, and pepper to taste.
03 - Heat a skillet over medium-high heat. Add fresh spinach and sauté briefly until just wilted, about 1-2 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 slices, and ham or mushrooms.
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 a spoon. Carefully crack one egg into each well. Lightly season eggs with salt and pepper.
07 - Place ramekins in preheated oven and bake for 20-25 minutes, until egg whites are fully set but yolks remain runny. Adjust baking time by 2-3 minutes for firmer yolks if desired.
08 - Remove from oven and immediately garnish with chopped fresh chives or parsley. Serve hot directly in ramekins.