स य इच्छेत् पुत्रो मे शुक्लो जायेत वेदमनुब्रुवीत सर्वमायुरियादिति क्षीरौदनं पाचयित्वा सर्पिष्मन्तमश्नीयाताम् ।ईश्वरौ जनयितवै ॥६,४.१४ ॥
In plain words
He who wishes, "Let a son be born to me who is fair, who will recite one Veda and attain the full term of life" — let the two of them have rice cooked in milk prepared, and eat it with butter. They are then able to beget.
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· bhāṣya
स य इच्छेत्— पुत्रो मे शुक्लो वर्णतो जायेत, वेदमेक- मनुब्रुवीत, सर्वमायुरियात्— वर्षशतं क्षीरौदनं पाचयित्वा सर्पिष्मन्तमश्नीयाताम् ईश्वरौ समर्थौ जनयितवै जनयितुम् ॥
In plain words
'If a man wishes' for a son fair in complexion, who masters a single Veda and lives his full hundred years, then the couple should eat rice cooked in milk with ghee — and this makes them able, truly able, to bring such a son into being.
Close to the Sanskrit
'If he should desire': 'may a son be born to me, fair in complexion, may he master a single Veda, may he attain his full lifespan' — a hundred years — [then], having had rice cooked with milk, the two should eat it with ghee; [thereby] they become capable, able, of begetting [such a son].