Take puff pastry out of the freezer and let it thaw in the refrigerator for about 1 hour. Preheat your oven to 400°F (205°C) and grease your baking dish or muffin tin with unsalted butter.

In a medium skillet, melt 1 tablespoon of butter over medium heat. Add diced shallot and minced garlic, sautéing for about 2 minutes until translucent. Toss in fresh spinach and sauté until wilted, seasoning with salt, pepper, and nutmeg; drain excess moisture.

Roll out the thawed puff pastry on a floured surface until 1/8 inch thick. Cut squares or circles and place one layer in each prepared muffin tin or baking dish. Layer with Gruyère cheese followed by sautéed spinach and prosciutto. Repeat, leaving space in the center for the egg.

Pour a splash of heavy cream into each pastry nest. Crack an egg into the center of each, ensuring the yolk stays intact. Season with Parmesan cheese, remaining Gruyère, chives, salt, and pepper before sending them to the oven.

Bake in the preheated oven for approximately 12-18 minutes until egg whites are set and yolks are glossy and slightly soft. Adjust baking time based on your preference, checking for doneness after the first 12 minutes.

Once baked, let the Baked Eggs Napoleon rest for 2-3 minutes to firm up. Garnish with fresh herbs and black pepper before serving.