Bring water with butter and salt to a boil. Remove from heat, add the flour and stir with a wooden spoon. Add the egg and stir immediately.
Let it cool to room temperature, cover the dough with cling film and refrigerate for at least one hour.
In the meantime – prepare the cheese filling (you may need to double the amount but start with this basic recipe and if you need more – prepare it later). Mix all the ingredients together and refrigerate.
Divide dough and roll it out on a well-floured board. Make sure the dough is very thin but not paper-thin, as it has to hold the filling and not rip while cooking.
There are two options at this point: You can cut 2.5X2.5 inch squares to create triangular shaped Kreplach or Cut 2.5 inches (6.5 cm) circles with a cookie cutter or a glass to create tortellini-shaped dumplings.
Place a teaspoon of filling in the center of the square and fold the dough over the filling to create half a circle. Press gently with your fingers to seal the dumpling.
Place on a well floured pan and freeze for at least half an hour.
At this point you can store the Kreplach in plastic bags or boxes and freeze until using.
Bring a pot of water to a vigorous boil, add 1 tablespoon salt, drop in the kreplach, and cook for about 10-15 minutes.
Place in a serving dish, drizzle with olive oil or melted butter, sprinkle Parmesan cheese and voila !