Sauté the Onion & Garlic. In a skillet over medium heat, warm a drizzle of oil or butter. Sauté diced onion until translucent, then add minced garlic for about 1 minute.
Cook the Spinach. Add fresh spinach leaves (or thawed, drained frozen spinach). Sauté until wilted (if fresh) or heated through (if frozen). Season lightly with salt and pepper.
Mix in Cheese. Remove from heat and stir in crumbled feta or shredded cheese (like cheddar) until combined. Allow the mixture to cool slightly.
Thaw the Pastry. If using store-bought puff pastry, ensure it’s fully thawed according to package instructions.
Cut into Squares. Lightly dust a work surface with flour. Roll out the puff pastry and cut into squares (about 3–4 inches each).
Fill & Fold. Place a spoonful of the spinach filling onto each square. Fold the pastry over (into a triangle or rectangle), pressing edges to seal. Crimp with a fork for a decorative touch.
Preheat Oven. Set your oven to 400°F.
Brush with Egg Wash. Beat one egg in a small bowl. Brush the pastry tops lightly for a golden finish.
Bake. Arrange the puffs on a parchment-lined baking sheet. Bake for 15–18 minutes, or until golden brown and puffed.