Lemon and Strawberries: "One bite" mushroom mini pies

These little mushroom filled bites burst with taste in your mouth! They're perfect snacks when you just want to grab something fast, when you're going to a picnic, when you want something to go with your beer or at any other time.
Invented as a savory trait I needed to prepare for an event, they've become a "must-have" appetizer in my cookbook and are one of the favourites.

INGREDIENTS (for about 40 pieces):

350g flour
20g fresh yeast
1 glass milk
50g butter
1tbs sugar
2tsp salt

FILLING:

400-500g mushrooms
1 onion
1 egg
2-3tbs bread crumbs
salt, pepper
1-2tbs olive oil for frying

Dissolve yeast in a glass of warm milk with sugar and set aside for about 15 minutes in a warm place to get them to work. Mix flour with salt and soft butter and add the yeast mixture. Knead the dough, until it's smooth and flexible and doesn't stick to your fingers. Form it into a ball, cover with a cloth and set aside to grow for about 1-1,5 hour in a warm place.

While waiting for a dough to be ready, prepare the filling:
Preheat olive oil on a pan, add finely chopped onion and fry until it becomes semi-transparent. Add mushrooms cut into small pieces.

Add salt and pepper and fry until mushrooms get soft - about 10-15 minutes. Take off the heat and when its cool add the egg, bread crumbs and mix all the ingredients well.
Preheat your oven to 200°C (392°F).
When the dough has doubled its size, roll it out into a big, thin rectangle. I divided the dough in half and did it one by one, but if you have enough space, you can do it all at once.
Next, put the filling in the middle of your dough, fold upper edge to cover the filling and roll it gently to create a long cylinder. Take a sharp knife and cut it into 3cm mini-pies.