There are multiple artists with this name:
1) Black Milk, is a hip hop producer and MC from Detroit, Michigan.
In 2004 he formed B.R. Gunna with Young RJ, and Fat Ray, and together they released Dirty District: Vol. 2, a follow up to a compilation released in 2001 by Slum Village, which he had contributed production to. Black Milk released a solo album, Sound of the City, the following year and in 2006 he signed a record contract with Fat Beats Records. In the fall of 2006, he released an EP, entitled Broken Wax. March 13, 2007 he released a second album, Popular Demand.
In addition to Slum Village, Black Milk has worked with the likes of J Dilla, Elzhi, Phat Kat, Frank-N-Dank, Lloyd Banks, Canibus, and Pharoahe Monch, and handled most of the production on T3's Olio mixtape of 2006.
In the Winter of 2007/2008 Black Milk paired with Aftermath recording artist Bishop Lamont to release a mixtape entitled Caltroit, which was nominated for Best Hip Hop Mixtape at Justo's Mixtape Awards.
Black Milk released an album with Fat Ray entitled The Set Up on March 4, 2008. His second solo album Tronic was released on October 28, 2008. He also handled the majority of production on Elzhi's album The Preface, released August 12 2008.
On December 25, 2009, he leaked the first single from his album Album Of The Year, the song is called Keep Going. He has also released two more singles named Welcome (Gotta Go) and Deadly Medley featuring Royce da 5'9" and Elzhi.
3) Western Australia's Blackmilk (yes, one word according to their CD metadata) are an indie/alternative group.
4) Black Milk were a girl band from Czech Republic. Members were: Helena Zeťová, Tereza Kerndlová a Tereza Černochová.