Preheat the oven to 375°F (190°C), or 170°C if using a fan oven, and lightly spray the cups of a muffin pan with non-stick spray.
In a large bowl, combine cream cheese, feta cheese, parmesan cheese, egg, spinach, dill, garlic, and black pepper. Stir well to combine.
Unfold your puff pastry sheet on a lightly floured surface, and roll it out just to remove any creases.
Using a sharp knife or a pizza cutter, cut the puff pastry sheet into 9 squares and press them into your prepared muffin pan (stretch each square a little if needed).
Divide the filling between the muffin cups, then to seal them bring all 4 edges of each puff together and press to seal.
Using a pastry brush, lightly brush each puff with egg wash.
Bake in the preheated oven for about 20 minutes, or until puffed and golden brown. Remove from the oven, allow to cool in the pan for 10 minutes, then with a knife loosen the edges and remove the puffs onto a wire rack to cool completely.