Line a strainer with a coffee filter and add the yogurt on top.
Place the strainer over a bowl and have it sit in the fridge for about four hours. I left mine overnight. Yogurt becomes very thick and separates extra liquids.
You can see the difference in yogurt texture in the first two pictures.
Place four sheets of fillo dough on top of each other, cut dough into 2"x2" cubes.
Rotate each sheet to distrubite the corners evenly. Using mini cupcake tray, place each stack of dough into its individual cup. Whisk egg with sugar. Using pastry brush, lightly spread egg mixture into each cup.
Bake them at 350F for about eight minutes or until folder brown.
Using a spoon, fill in each cup with yogurt. Top it off with chocolate or fruits. Serve them right away, otherwise cups can get soggy. Optionally, you can sprinkle tartlets with powdered sugar.