Preheat the oven to 400 degrees F and line a baking sheet with parchment paper.

Unfold the thawed puff pastry sheet on a lightly floured surface and cut it into 8 equal rectangles.

In a small bowl, stir together the pesto, mozzarella, and Parmesan until evenly mixed.

Place a spoonful of the cheese mixture in the center of each pastry rectangle.

Beat the egg in a small bowl and brush the edges of each rectangle with egg wash.

Fold each rectangle over the filling to form a square and press the edges with a fork to seal.

Place the puffs on the prepared baking sheet and brush the tops with the remaining egg wash.

Add two olive slices to the top of each puff to create ghost eyes.

Bake for 15 to 18 minutes until the pastry is golden and puffed.

Remove from the oven and let cool for 5 minutes before serving.