Preheat oven to 400ºF.
Heat oil in a sauté pan on medium high. Add diced onions and sweat for about 5 minutes.
Add garlic and spinach and cook for another 3 to 5 minutes.
Place spinach into a medium bowl and then stir in the cheeses, yolk and salt.
Cut a puff pastry into 3 to 4 inch squares and spread 1 tablespoon of filling in a line along the center.
Brush egg wash along the edges and then seal the two sides together to create a 'cone' shape.
Bake for 15 to 17 minutes.
