Preheat your oven to 375°F (190°C).

In a large skillet over medium heat, melt a small amount of butter or oil. Add diced onions and minced garlic, sautéing until onions are translucent, about 3-5 minutes.

Stir in chopped mushrooms, cooking for around 5-7 minutes until softened and moisture is released.

Fold in fresh spinach and sauté until just wilted, about 2-3 minutes. Season with salt and pepper, then remove from heat and let cool.

Combine the cooled mushroom and spinach mixture with cream cheese and chosen cheese in a mixing bowl, stirring until cohesive.

Lightly flour your work surface and roll out the puff pastry to about 1/8 inch thick. Cut into 24 squares.

Place about a teaspoon of filling in the center of each square, leaving room around edges for sealing.

Fold each pastry over the filling and press edges together, crimping with a fork to seal.

Whisk an egg to create an egg wash and coat the tops of each pastry with it.

Arrange on a parchment-lined baking sheet and bake for 20-25 minutes until golden brown and puffed.

Allow to cool for a few minutes before serving warm.