Ashlee Simpson: One Hot Mama!

Pete Wentz and Ashlee Simpson Wentz spent New Year's Eve feeding each other cake at Pure in Las Vegas but she's still determined to shed 15-20 pounds of baby weight.

Ash has started to watch what she eats," a pal of Ashlee, 24, and Pete, 29, whose son, Bronx Mowgli, arrived Nov. 20, tells OK!. "She's doing five small meals a day and trying to lay off carbs and sugar. She might be overdoing it with 20 pounds, but she wants to lose a little extra so when she has pizza it won't make a difference."

Ashlee, who recently dyed her red locks back to blond, recently reflected on 2008, calling it "the greatest year of my life. "I don't know if I can have high expectations for 2009 because 2008 was so good."

Of her newborn son, Bronx, Ashlee said, "He's the best thing that has ever happened to me."