“Short’nin’ Bread” is a song from the Minstrel Show tradition.  It’s considered racist because of the words. 

To be clear the history of the song swings wildly from not racist to racist and back again. It started as a folk song sung by slaves in the south and in that regard it is in no way racist.    What is racist on the other hand is when several white musicians later dressed in black face and performed several very very racist songs with the lyrics tweaked.

“Shortnin’ Bread” is a plantation song.  Its first written version was captured by poet James Whitcomb Riley in 1900.  Like the Brothers Grimm (die Brüder Grimm or die Gebrüder Grimm), Jacob (1785–1863) and Wilhelm (1786–1859), were German academics, philologists, cultural researchers, lexicographers, and authors who together collected and published folklore. 

Songs like “Shortnen Bread” and “Pick a Bale of Cotton” are traditional American folk field songs, sung more than likely by slaves, whose real origins are lost. The most known version of this piece were recorded and performed by people like Huddle William Ledbetter more commonly known as “Lead Belly” to keep their stories alive and to relate to his own experiences of picking cotton.

|: Mammy's little baby loves short'nin', short'nin'
Mammy's little baby loves short'nin' bread :|

Fetch that dough, from the kitchen shed.  
Rake those coals out, hot and red
Put on the oven and put on the lid.  
Mommy's going to cook some short'nin' bread. Ref.

Three little children, lying in bed.  
Two was sick and the other 'most dead
Send for the doctor and the doctor said. 
"feed them children on short'nin' bread."  Ref.

When those children, sick in bed, 
heard that talk 'bout short'nin' bread.
They popped up well, to dance and sing, 
skipping around cutting the pigeon wing. Ref.

Pull out the skillet, pull out the lid,
Mama's gonna make a little short'nin' bread
That ain't all she's gonna do, 
Mama's gonna make a little coffee too  Ref.