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.

From TMZ.com

Thumbnail via TMZ.com