Here are some pierogi tips and tricks, enjoy! :)
It is much easier to glue pierogi before cooking, if you moisten half of the edge of a dough circle with some water. Also remember that any air should be left inside pierogi. Otherwise it will tear during cooking. Keep an eye on it.
Some people add a yolk to a pierogi dough. There is only one effect: pierogi dough is a little bit tough and 'cartilaginous'. Usually original Polish pierogi dough is made without eggs (I do it this way also). That makes pierogi more delicate and soft.
50%-75% of water we use to prepare a pierogi dough can be replaced by milk. A dough will be more delicate and its taste fits great all sweet fillings: fruit and a sweet curd cheese. It is also possible to use slightly sweetened milk (about half a teaspoon of sugar per 1 glass of milk).
We should cook pierogi in water with an addition of some oil, so that they don't get glued together. The second very important thing is to throw pierogi onto boiling water. It means that you should not throw a sackful of pierogi (particularly frozen ones!), and let water to cool down. If you have a lot of pierogi to cook use larger pot and a lot of water. Otherwise cook pierogi in few smaller batches.
A fact that pierogi is not a dish which is possible to be prepared hastily can be a certain problem for some people. Admittedly, making pierogi step by step is a bit time-consuming. Personally, I usually make a lot of pierogi at once and freeze a considerable part of them on some other time (see tip 6). On the other hand, there is a lot of pierogi makers in stores with household stuff. This utensil is to speed up your pierogi sealing - quite a good idea, indeed. The quality of models varies. Those cheaper, plastic pierogi makers are particularly prone to break during operation. I think it is worthwhile buying a better, metal utensil. Typical price is from 10 up to 20 dollars. Remember to grease a surface of a pierogi maker, so that the dough does not stick.
Pierogi are perfect for freezing (however, do not freeze raw pierogi dough). All you need to know is how to freeze pierogi. Since not boiled raw pierogi like to crack in a freezer, it should be slightly boiled first (this is a so-called blanching). Throw pierogi into a pot with boiling water + some salt + 1 spoonful of oil. Stir and wait until they sail out. Then, immediately catch pierogi and throw into the second pot with very cold (or icy!) water containing 1-2 spoonfuls of oil. It is important - please notice that we do not cook pierogi after sailing out (we do that only with pierogi that are going to be consumed). Now wait a while and arrange cooled pierogi on a serving tray. Put it into a freezer. When frozen, throw pierogi into plastic bags for the sake of convenience. We heat up home-made frozen pierogi by ordinary cooking in water (heating in microwave oven is also possible but I don't recommend it). Be careful not to cook them too long. Frozen pierogi keeps the taste, freshness and sustenance. In contrast with a ready-made pierogi from a grocery store, these are suitable for additional frying.
Lithuanian housewives have a wonderful patent for savory pierogi dough. They use onion juice instead of water. The taste is great!
In Polish restaurants and pierogarnia one can come cross a colorful pierogi. You too can make orange, yellow, green and pink dough at home. Piece of cake! To make yellow pierogi add some turmeric during kneading the dough. Orange, green and pink pierogi dough is made by replacing some water with a carrot, spinach or red beetroot juice respectively.
I love bilberry and blueberry pierogi for this juicy squirting while eating ;) But if you find it a problem I have two tips for you. First. Add a bit of potato starch to bilberries mixed with sugar. During cooking potato starch will thicken the content of pierogi. Thanks to that, instead of juice we will have a dense sauce inside. Now, the second trick. Do not add sugar to blueberries. Sugar takes the juice out of fruit. When you make such not-sweetened pierogi remember to prepare some additions (e.g. cream or ice-cream) sweet enough.
The peak of the culinary artistry (and dedication!) is to make pierogi with a so-called braid aka frill (see photo at right). In order to make such a beautiful pierogi first fold and seal it with your fingers as usually. Now, the first step is to raise one of two corners, bend it and stick by pressing to the pierogi edge underneath. Next, move a little further (towards the center) and once again: raise a dough (forming a frill), bend it and stick. Doing it step by step you will make a beautiful braid along the entire length of the edge. Good luck!