The 30-year-old singer’s empire took in $750 million dollars last year and is may reach $1 billion dollars. The sun sets extra early one sloppy winter afternoon on the clutch of paparazzi huddled on a midtown sidewalk beside an idling SUV. Big, wet flakes of snow are landing on cameras, heads, shoulders, but the photographers are still there, bouncing up and down against the chill. They’ll keep on bouncing all night if they have to, because inside is Jessica Simpson, and at a certain point, she’s going to have to come out.

But on the fifteenth-floor showroom of the Jessica Simpson Collection, it is warm and bright and Simpson is in no hurry. Everywhere are mannequins in denim cutoffs, platform sandals, crochet tops, as if dressed for some sort of outdoor-music festival in Nashville or Dallas or Baton Rouge. Eight women (including Simpson; her mother, Tina; and her mother’s best friend, Beth, who was Jessica’s first dance teacher back in Richardson, Texas) are clustered around a big square table covered with hats—all sorts of hats. There are beret-style hats and fedora-style hats, and lots of versions of brimmed, military hats in patterns ranging from camouflage to houndstooth to what looks like a felted patchwork quilt. Every single hat is examined as it fits over Simpson’s flossy, long blonde hair, its details scrutinized: Too much brim? Too little? How about this but in mustard yellow here and olive green there? Notes are taken, style numbers read aloud and entered into a laptop computer. And then, every so often, Simpson, her voice still guttural and Texan: “Approved!”

These hats are a piece of Simpson’s fashion empire, which clocked sales around $750 million last year. This year, Simpson, who is 30, will add both a full ready-to-wear collection as well as a “career separates” line to her docket, which should push sales past the billion-dollar mark. And Simpson—or Simpson’s top surrogate, her mother—will sit in a room just like this to approve every single thing that gets her label inside.

To put that figure in context, it means Jessica Simpson is doing roughly the same volume in sales as Michael Kors.

It’s a dizzyingly enormous amount of stuff, and it’s a staggering amount of money. And at the center of it all is … Jessica Simpson? We first met her about ten years ago, when she was a virgin from the Bible Belt. The daughter of a minister, she started recording gospel albums when she was 14—someone had been impressed by a performance she gave at Bible camp.

We got to know her better when she married the best-looking member of a boy band, Nick Lachey, and documented her charmingly clueless life as a newlywed in a reality show on MTV. She’d talk about farting, reveal her ability to burp the alphabet, and wonder how poultry could be seafood (“Chicken of the Sea”).

Simpson and Lachey split up in 2005, and her tabloid appeal exploded as she began dating a string of famous men (last year, John Mayer told Playboy his relationship with her was like “sexual napalm,” which was apparently a good thing) and allowing her weight to fluctuate more than is normal for very famous girls.

And while this was all going on—while she was dating and then not dating football players—she was focused on building Jessica Simpson the Brand. “I never thought I’d be some fashion mogul!, ”she says, laughing her big, open-mouthed laugh. The unlikeliness of it all is probably the exact reason why it works so well.

Celebrity lines are usually doomed to failure; they’re the cautionary tale of the aughts. Sarah Jessica Parker’s attempt to go mass with her Bitten line didn’t work, and her struggle with Halston is just that—a struggle. Lindsay Lohan’s foray into leggings has been less than impressive, and her attempt to consult for Ungaro became an industrywide joke. Success in celebrity fashion has been for the extremely rarefied microbrands: the Olsen sisters’ the Row, for example, or Victoria Beckham’s small collection of very small dresses. These are clothes every bit as expensive, well made, and sophisticated as what the members of the celebrity universe borrow and buy from the biggies, but it’s not clear that anyone is really making much money off these lines, even if they sell well at places like Barneys Beverly Hills or Neiman Marcus.