The Compendium of Bheḷa 6.4.35

6.4.35

vipācayejjaladroṇe caturbhāgāvaśeṣitam | tatkaṣāyaṃ jalaṃpūtaṃ ghṛtaprasthaṃ vipācayet ||

one should cook in a droṇa of water until reduced to a fourth part. / In that strained decoction water, one should cook a prastha of ghee,