DON’T call Jessica Simpson a ditzy blonde!

The mom of two is bright enough to head a billion-dollar business empire and has no intention of being taken to the cleaners by her baby daddy Eric Johnson.

She not only wants Eric to sign an iron-clad prenup but also get a job before walking down the aisle, said a source.

“Jessica’s number one pri­ority is her children and their financial future – not Eric,” said the source. “She’s the family breadwinner with the most at stake if they split.”

The 33-year-old beauty is a Weight Watchers pitchwoman and one of Hollywood’s hottest brands, selling shoes, swim­wear, perfume and luggage under her name.

She and former NFL player Eric, 34, got engaged more than three years ago, and since then she’s given birth to daughter Maxwell, 20 months, and son Ace, 6 months.

But Jessica, who boasts a personal fortune of $100 mil­lion, and Eric have yet to set a wedding date.

 “Things keep changing,” said the source.

“Jessica’s business empire is ex­panding, and when she had kids, it became even more important to get an iron-clad prenuptial agreement in place.

“Jessica’s got an army of legal eagles at work, updating that prenup.

“It doesn’t help that Eric has been unemployed the entire time they’ve known each other, and he doesn’t seem to have any plans to get a J-O-B. Let’s face it, his job is being Mr. Jessica Simpson – even though they’re not even mar­ried yet.”

Eric, a tight end, played football at Yale University and was drafted by the San Fran­cisco 49ers in 2001. But injuries kept him out of the 2003 and 2005 seasons, and he was released by the New Orleans Saints in 2008 after only one year.

He proposed to Jessica one month after his di­vorce from first wife Keri was finalized, but Jessica report­edly purchased her own five-carat ruby engagement ring.

When Eric and Jessica got engaged, he reportedly had big plans to open a chain of vegan restaurants or launch some other business enterprise.

But those plans never material­ized, and these days the jobless hunk sports unkempt hair and a scruffy beard as he accompanies Jessica around, often toting Maxwell or Ace.

“On one hand, Jessica thinks Eric is a great father, but she wants him to earn his own living,” said the source. “If that doesn’t happen, she has no problem keeping her unmarried status.”