Poland - żurek (soup with any meat bouillon at the rye flour's sourdough)
the best with boiled egg, cooked potato chopped in cubes and chopped smoked sausage in slices. the best thing ever: sour, a little sweet and salty
Honorable mention: pierogi (dumplings), especially Kievan/Rutherian pierogi (with cottage cheese, potato and a little bit of onion)