Preheat the oven to 450°F / 230°C.
Heat a pan with some olive oil over medium-high heat and, once hot, add the chopped onion. Cook for about 3 minutes, and then add the crushed garlic. Sauté for about 30 seconds or until fragrant.
Add the roughly chopped spinach with a pinch of salt and pepper, and sauté for a few minutes. Remove from the heat and set aside.
Fry the bacon until nicely browned. Let it cool, then chop into small bite-sized pieces.
In a mixing bowl, beat the egg, add the cream cheese, and continue mixing it until well combined. Stir to combine. Season it with salt and pepper and add the chopped dill, the cooked spinach mixture, feta cheese, finely chopped bacon, and parmesan cheese.
Flour your work surface, and using a rolling pin, lightly roll out your puff pastry to take out the creases. Cut the sheet into 3–4-inch squares and place them on a parchment-lined baking sheet.
Add about 1-2 tbsp of the mixture to each square of puff pastry. Beat the egg yolk in a separate bowl and use that to brush two edges of the puff pastry. Crimp the egg-washed sides together. Repeat this for all of your pastries.
Place the baking sheet in the fridge for 15 minutes. Once chilled and set, remove from the refrigerator and brush each pastry with egg wash. Place in the oven for 20 minutes.
Once golden brown and crisp, remove from the oven. Leave to cool and serve and enjoy!