01 - Preheat oven to 375°F. Lightly grease four individual ramekins or one medium baking dish.
02 - Melt butter in saucepan over medium heat. Whisk in flour and cook 1 minute. Gradually add milk, whisking constantly until thickened. Stir in Gruyère cheese, nutmeg, salt, and pepper. Remove from heat.
03 - Sauté spinach in skillet until just wilted, about 2-3 minutes. Remove from heat.
04 - Place puff pastry or brioche slice in bottom of each ramekin. Layer with sautéed spinach, zucchini slices, tomato, and ham or mushrooms.
05 - Spoon cheese sauce evenly over layered vegetables and ham in each ramekin.
06 - Create shallow well in 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 for firmer yolks if desired.
08 - Remove from oven. Garnish with fresh chives or parsley. Serve immediately while warm.