01 - Preheat the oven to 375°F. Lightly grease four individual ramekins or one medium baking dish.
02 - Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1 minute. Gradually add milk, whisking constantly until sauce thickens. Stir in Gruyère cheese, nutmeg, salt, and pepper. Remove from heat.
03 - Briefly sauté spinach in a skillet until wilted, approximately 2-3 minutes.
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 for vegetarian option).
05 - Spoon prepared cheese sauce evenly over the layered vegetables and ham in each ramekin.
06 - Make 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 egg whites are set but yolks remain runny. Adjust baking time for firmer yolks if desired.
08 - Remove from oven and garnish with fresh chopped chives or parsley. Serve immediately while hot.