The riddle describes two words. The first part, "Лягу я под дверью дома твоего" (I will lie under the door of your house), suggests the word "ПОРОГ" (threshold). The second part, "На тарелку лягу в праздничны" (I will lie on a plate on holidays), suggests the word "ПИРОГ" (pie). Therefore, the answer is ПОРОГ ПИРОГ.