When Kimbal Musk, 40, and his brother Elon sold their first company, Zip2, in 1999 for more than $300 million, both of them could have spent the rest of their lives doing little more than surfing and spending money.

Instead, they kept on working. Elon started PayPal (in which Kimbal was a big investor) and unloaded it for $1.5 billion in stock, then he launched Tesla Motors , the electric car company, and Space X, a commercial space-exploration venture. Elon’s latest concept, Hyperloop, would transport people between major cities at speeds of more than 700 mph.

Kimbal went to cooking school, moved to Boulder and worked for chef Hugo Matheson at the restaurant Mateo on Pearl Street. He then opened The Kitchen restaurant with Matheson. The team opened another, and another. Now, The Kitchen is on track to have seven restaurants within the next year or so — with more, surely, on the way — and Musk is responsible for a fast-growing nonprofit organization called Learning Gardens that puts gardens in school playgrounds.

Despite the money and success, Kimbal Musk doesn’t broadcast a sense of entitlement. The tall South African handles a good bit of his own public relations, which is not typical. He hangs out in the restaurants and talks food. A big chunk of his life revolves around his three kids and two younger half-sisters. The bunch of them live in a big Victorian house near downtown Boulder. He is divorced from Jen Lewin, a designer who helped found The Kitchen and with whom he remains close.

With more Kitchen restaurants popping up along the Front Range, and with Learning Gardens growing at such a fast clip around the country (Musk said by the end of the year, the nonprofit should reach more than 100,000 kids every school day, from Chicago to Denver to Los Angeles and beyond), we wanted to get to know Musk a little better.

He grew up in an ambitious household, with Elon and bunches of cousins. For kicks, he built computers. His mother was a prominent dietitian, and his father had his own engineering practice.

“We had an independent upbringing,” said Musk. “Our parents were very busy. Not like a regular person’s job, but consumed. It left us to go figure out our own passions. It was a challenging upbringing, but I wouldn’t do it differently.”

From the beginning, he was entrepreneurial.

“I’ve only worked for someone else once in my life,” he said. “I did it for three months and I spent most of my time working on my business plan with my brother. I did my work, but I was done by 10 o’clock in the morning, so I would turn to my business plan.”

Today, he works seven days a week, but squeezes in a lot of family time. The every-day schedule, he said, gives him more freedom to be with family because he’s not spending long hours five days a week away from home.

We recently drove with him in his Tesla sedan — he and Elon are tight, and he sits on the Tesla board — to Cowell Elementary School, where one of his Learning Gardens has been installed, and then spent time with Musk at his downtown Denver Kitchen restaurant. He ate a new pasta dish on the menu and a plate of charcuterie while we chatted on a sidewalk-fronting patio.

The first thing he wanted to talk about was 9/11.

Kimbal Musk: I saw the World Trade Centers burning. With the planes in them. I was on Canal Street when they fell. It was like seeing the Flatirons collapse — it was outside of reality. Reality crumbled when that happened.

Question: How did the experience change you?

Answer: I had recently graduated from the French Culinary Institute (now called the International Culinary Center), and I lived 10 blocks away from Ground Zero, so I was able to go beneath the security curtain seven days later to cook for the firefighters. I ended up cooking for six weeks out of the kitchen of a destroyed restaurant. Out of all of the things that have happened in my life, that was the reason I moved to Boulder and opened a restaurant. Serving the firefighters was the only way to connect to that community. We would find fish from fishermen who had nowhere to sell it. The experience taught me the value of community.

Q: Community is a big part of what you do — you even call your group of restaurants The Kitchen Community. How did Boulder become your new community?

A: I did a tour of the West — Jackson Hole, Boulder, Denver, Santa Fe, San Diego, Laguna Beach, Los Angeles, the Bay Area, Marin County, Portland, Seattle. I did it in February — I’m a big weather guy — and I wanted to see what these places were really like. Boulder is an amazing place in the winter. The rest of the places were just OK. So we rented a house for the summer, and that was that.

Q: You were a tech guy. Why cooking? A restaurant?

A: Growing up, I was the cook for the family. I loved it, loved the tactile side, the creative side, the reaction. The creativity gets me excited. The way we work at The Kitchen, the greens you get today won’t be the same as the greens you get tomorrow. You have to have talent, you have to adjust. They could be tougher. You have to know how to blanch them a little bit longer, or you might have to use a little bit more or less olive oil.

Q: What is The Kitchen food, to you?

A: What we try to be is real food, and real food is simply a lot healthier. But we aren’t out to make “healthy food.” Our pork sandwich might be the tastiest thing on the menu. We try to keep it local. We had only a lamb burger, rather than a hamburger, for a long time, although now we use great local beef for hamburger. We buy three cows every two weeks from Koberstein Farms in northern Colorado and we split them up between the restaurants. The community aspect is important to The Kitchen. For example, we don’t do take-out. We don’t like people eating food to go. We prefer people sitting down and eating.

Q: Why gardens?

A: It’s entirely about connecting kids to real food, about finding a way to do it that would scale. We helped this great Longmont nonprofit, the Growe Foundation, build up a network of 16 gardens, and it was tough to scale. We created something that is easily built, something that — and this is very important — kids want to play in, where teachers want to teach.

Q: What is your favorite possession?

A: I have a handmade Japanese knife. It never needs to be sharpened. It’s the most expensive knife I’ve ever bought. I use it every day.

Q: What is the most overrated virtue?

A: Selflessness. You need to look after yourself, so you can take care of others.

Q: What is your favorite way to pass time?

A: I love to cook. It’s the best way to get the family together.

Douglas Brown: 303-954-1395, djbrown@denverpost.com or twitter.com/douglasjbrown