For the dough, mix the flour and salt in a bowl and the oil and warm water in a jar. Then add the liquid to the dry and knead until soft. It will feel too dry at first but don't worry it's not - just keep kneading.
When the dough is homogenous and soft, cover it and let it rest at room temperature for about 40 minutes to 1 hour.
For the filling, cut the onion veeery finely using a grater or a food processor so you get it so fine it's almost a paste.
Then mix the onion with all the other filling ingredients. Get your hands diry - it's a lot of fun pressing the mixture through your fingers ;)
Now roll out the dough until it's so thin iti's almost see-through (about 1mm thick). Cut out 5-7 diameter circles. (Tip: If you don't have a cookie cutter of that size, use a glass that has the desired diameter on top and is not tooooo thin and fragile ;))
To fill the dough, take on circle into one hand, place 1 tsp of filling in the middle of it, fold the dough over it so that it's folded in half. then take the two corners and pull them towards each other so you can stick them together. (A good video showing it can be found here: https://youtu.be/U9maYccMD-I?t=237)
At this stage you can freeze them, just make sure you lay them out flat next to each other in the freezer bag or tray so they don't stick to each other too much.
Now for boiling there shouldn't be too many pelmeni per pot because else they'll cool the water down too much and won't have enough space to float around. So iI recommend preparing a pan of boiling water for each pair of two portions. So if you plan on eating all 6 portions right away, fill 3 pans with boiling water. To each pan add 1tsp of salt, 1/2 tsp pepper and 2 bay leaves. Add the pelmeni and boil them on medium heat for about 30 minutes. Make sure they don't start sticking to the bottom of the pan while cooking.
Get the pelmeni out of the water carefully, plate them up with the sour cream and dill and enjoy them right away :)