01 - Preheat the oven to 375°F. Lightly grease four individual ramekins or a medium baking dish with butter or cooking spray.
02 - Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1 minute to form a roux. Slowly pour in milk while whisking constantly. Continue whisking until sauce thickens and bubbles. Stir in Gruyère cheese, nutmeg, salt, and pepper until cheese melts. Remove from heat.
03 - Heat a skillet over medium-high heat. Add spinach and cook briefly until just wilted, about 1-2 minutes. Remove from heat.
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 slices.
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. Crack one egg into each well. Lightly season eggs with salt and pepper.
07 - Bake for 20-25 minutes until eggs are just set but yolks remain runny. Adjust cooking time slightly for firmer yolks if preferred.
08 - Remove from oven and garnish with freshly chopped chives or parsley. Serve immediately while hot.