Add the spinach to a large pan over medium heat and toss until fully wilted.

Transfer the cooked spinach to a fine mesh strainer to cool, then squeeze out as much water as possible.

Sauté the onions and garlic in your choice of fat over medium-low heat until translucent and fragrant, about 3-5 minutes.

Turn off the heat and stir in the herbs. Roughly chop the spinach and add it to the bowl with garlic, onion, herbs, feta, and a pinch of salt; mix to combine.

Roll out the puff pastry to about ⅛” thick, brushing off excess flour.

Add the spinach-feta mixture to the top of the pastry, spreading it evenly, leaving a ½” space at one end.

Using a little water on the exposed pastry edge, roll the pastry tightly and pinch to seal.

Roll the log back and forth a few times, then wrap in plastic wrap and chill for 15-30 minutes.

Preheat the oven to 400℉/205℃, and line a baking sheet with parchment paper.

Unwrap the log and slice into ½” rounds (about 16 pieces).

Space the pieces on the baking sheet and bake for 20-25 minutes until lightly golden.