Preheat the oven to 350 degrees Fahrenheit.
Finely dice the mushrooms, including both the caps and the stems. Dice the 1/2 onion. Combine the mushrooms, onion and olive oil in a skillet and cook over medium heat for approximately 5-7 minutes, until the onion is soft and translucent and the mushrooms have given off their liquid.
227 grams white button mushrooms, 1/2 yellow onion, 1/4 cup olive oil
Add the chopped up chestnuts, parsley and salt and pepper to the pan and cook, stirring constantly, for an additional 3 - 5 minutes.
1 ¼ cup chopped chestnuts, already roasted or steamed, 1/4 cup chopped flat leaf parsley, 1/2 teaspoon salt, 1/2 teaspoon ground black pepper
Place the contents of the frying pan in a bowl and allow to cool.
Beat the egg in a small bowl and once the mixture has cooled, add the egg to the mushrooms and chestnut mix. Stir well to combine.
1 large egg
Prepare your phyllo dough by cutting 3 inch strips of phyllo dough. Once you are ready to start making the triangles, take a double layer of phyllo and lay it in front of you. Brush with some olive oil (you don't want to soak it through, and it does not need to be brushed with olive oil all over).
1 lb phyllo dough
Place approximately 1 teaspoon of filling at the bottom of the phyllo strip. You are now ready to start making your triangles. Pay attention! :)
Take the bottom, left hand corner of your phyllo strip and fold it over the filling, bringing it to the right hand edge, just above where your filling ends. Then, take what is now the bottom right hand corner, and fold it over so that it reaches the left hand edge. Now move again to the left hand corner, and bring that to the right hand edge. Keep repeating. You will see that after a few movements, your triangle will start to take shape. Refer to the pictures above to help visualize what we are trying to describe. Repeat process to make more triangles.
Place your triangles on a parchment or non-stick mat lined baking sheet. Brush the tops of your triangles with a little more olive oil. Bake in the middle rack of your oven for 15 - 20 minutes, until golden brown on top and bottom. Remove from oven and allow to cool on a baking rack.
1/4 cup olive oil, for brushing phyllo
These mushroom and chestnut mezedes (appetizers) are best when served warm.
Enjoy!