Preheat the oven: Begin by preheating your oven to 375°F (190°C) to ensure it is fully heated and ready for baking once your tartlets are prepared.

Prepare the filling: In a mixing bowl, blend together thawed and drained spinach, crumbled feta cheese, grated Parmesan cheese, minced garlic, and mayonnaise. Stir thoroughly until all components are uniformly combined. Season with ground pepper according to your taste preference.

Prepare the Puff Pastry: Slice the pastry into petite squares that match the dimensions of the muffin tin holes.

Poke holes: Poke some holes in the bottom of each pastry square with a fork to keep them from puffing up too much during baking. This helps release steam and maintains the tartlet shells' shape.

Assemble the Tartlets: Scoop the spinach and feta mix into each puff pastry cup, making sure it's evenly spread. Be generous with the filling but leave a small space around the edges.

Bake to Perfection:Put the muffin tin in the preheated oven and bake for about 15-20 minutes, or until the puff pastry becomes golden brown, and the filling is bubbling.

Cool and Serve: Allow the tartlets to cool for a few minutes before carefully removing them from the muffin tin.