Jessica Simpson: "I Am So in Love With Baby Maxwell!"

Jessica Simpson

Jessica speaks! Er, tweets!

One week after she welcomed daughter Maxwell Drew Johnson, Jessica Simpson gave her 5 million-plus Twitter followers an update on her baby and first-time motherhood -- and all is very, very well!

"I am so in love with baby Maxwell," the singer and Fashion Star mentor, 31, wrote Tuesday. "I want to cry every time I look at her. Motherhood is by far the best thing I've ever experienced."

Maxwell, her first child with fiance Eric Johnson, arrived at Cedars-Sinai Medical Center in Los Angeles the morning of May 1, and weighed a whopping 9 lbs., 13 oz.

And, as Simpson recuperated at the hospital after Maxwell's arrival, her maternal instincts kicked in -- and then some!

"Everyone is marveling at what a natural Jessica is," a source told Us. "She was born to be a mom!"

Pick up the new Us Weekly, on stands Friday, for much more on Jessica's first days at home as a new mom -- Maxwell's over-the-top nursery, how she's gearing up to lose the baby weight, Johnson's comical diaper duties woes and more!