Śatapatha Brāhmaṇa ("of a hundred paths") 2.5.1.17

2.5.1.17

atha dyāvāpṛthivya ekakapālaḥ puroḍāśo bhavati | etairvai havirbhiḥ prajāpatiḥ prajāḥ sṛṣṭvā tā dyāvāpṛthivībhyām paryagṛhṇāttā imā dyāvāpṛthivībhyām parigṛhītāstatho evaiṣa etadya etairhavirbhiḥ prajāḥ sṛjate tā dyāvāpṛthivībhyām parigṛhṇāti tasmāddyāvāpṛthivya ekakapālaḥ puroḍāśo bhavati

Then follows a cake on one potsherd for Heaven and Earth. Now when Pragâpati had created the living beings by those offerings, he enclosed them within heaven and earth; and so they are now enclosed within heaven and earth. And in like manner he, who by means of those oblations creates living beings, thereby encloses them within heaven and earth: this is why there is a cake on one potsherd for Heaven and Earth.