Clean and wash the spinach. Peel and finely dice the onion and garlic. Heat the oil in a pot and fry the onion and garlic. Add the spinach dripping wet and let it collapse.
Season with salt. Put the spinach on a sieve and let it drain. Place puff pastry slices next to each other on a floured work surface and cut in half. Crumble the feta cheese into a bowl. Stir in sour cream and egg.
Season with salt and pepper. Roll out puff pastry pieces a little and fold corners 2/3 to the middle. First spread spinach, then cheese cream on top. Place one slice of turkey breast slices on each. Mix milk and egg yolk and brush the edges of the pastry with it.
Place the puff pastry particles on a baking tray lined with baking paper. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 20-25 minutes. Serve the puff pastry particles still warm.