Whomever Allah has given milk to drink, should say
اللّهُـمَّ بارِكْ لَنا فيهِ وَزِدْنا مِنْه
“O Allah, bless us in it and give us more of it.”
Allaahumma baarik lanaa feehi wa zidnaa minhu
At-Tirmidhi 5/506. See also Al-Albani, Sahih At-Tirmidhi 3/158