Jessica Simpson Thanks for the Mammaries

12/27/2012 3:43 PM PST

Jessica Simpson's new baby has hit the milk-dispensing JACKPOT -- and lucky for us, the singer's already giving out a sneak preview of the goods.

Jessica -- who's currently on vacation in Hawaii with her fiance and baby #1 -- just posted the ample photo on Twitter ... with the caption "Fun in the sun." And we have to agree.

Milk ... it does the body good.