Creating these tartlets is straightforward and fun. Follow these steps to prepare your Balsamic Glazed Mushroom and Spinach Tartlets:

1. Preheat the oven to 400°F (200°C).
2. Roll out the puff pastry on a lightly floured surface and cut it into small squares. Arrange the squares on a baking sheet lined with parchment paper.
3. In a pan, heat a drizzle of olive oil over medium heat. Add the minced garlic and sliced mushrooms, and sauté for about 5 minutes until the mushrooms are soft and fragrant.
4. Add the fresh spinach to the pan and cook until wilted. Pour in the balsamic vinegar and continue cooking for an additional 2 minutes to allow the flavors to meld.
5. Season the mixture with salt and pepper to taste. Remove from heat and let cool slightly.
6. Spoon the mushroom-spinach mixture onto each puff pastry square. Top each with a generous sprinkle of crumbled feta cheese.
7. Place the baking sheet in the oven and bake for 15-20 minutes, or until the puff pastry is golden brown and crispy.