If I'm going for the boiled ones (I personally prefer steamed), I go for a bit more elaborate dough version than standard flour and water, it's much tastier and easier to work with

• 1 kg flour
• 600ml water
• 100g butter

• 1 teaspoon salt

• mix flour and salt

• separately boil water with butter

• slowly trickle in thin stream the water with butter into the flour constantly mixing it

• wait a bit until cooled and knead it thoroughly

• leave it to rest for 30m

that's it.

as for the filling, my favourite is mashed potatos+lardons+dill or sauteed fresh cabbage with tomatos, tho poles usually go for mashed potatos+cottage cheese or sauteed sauerkraut+mushroom (meh)