In 2009, Natasha Case and Freya Estreller, both in their mid-20s, wanted to take their nascent ice-cream sandwich side hustle, Coolhaus, to the Coachella music festival to test the idea on a large crowd. "We went big, like go big or go home," Case tells CNBC Make It. "Almost like cart before the horse. You just do it, and you see what the response is." Before Coachella, Coolhaus was more of a hobby than a real business. They had sold their ice-cream sandwiches at a craft holiday fair, but that was about it. Case had studied architecture at Berkeley and got a master's in architecture from UCLA. Estreller graduated from Cornell and worked in real estate development. So the duo used those themes to name their creations: The "Frank Behry" was two sugar cookies with strawberry ice cream in the middle. The "Mintimalism" was two chocolate cookies stuffed with mint chip ice cream. To sell at Coachella, Case and Estreller needed a food truck. "So we found a beat-up postal van on Craigslist and bought it with my personal credit card," says Case. It cost $2,500. "The door didn't even open, and there were rails on the windows. It was amazing."

The van also didn't drive. So Case and Estreller had it towed from the Craigslist seller to Estreller's mom's house in Los Angeles. To get it to Indo, California, for Coachella, several hours away, the young business partners (and romantic partners, too) joined AAA Platinum — because new members got a free 200-mile tow. They drove themselves there in a minivan packed with chest freezers to keep the ice cream cold. The ice-cream sandwiches were a sensation at Coachella. They sold their sweets until 4 a.m., as festival attendees continued to party after the music ended. Case remembers a concert-goer waking her up at 7:00 one morning to tell her there was a line of people waiting for them to open up the truck. Case and Estreller earned enough money to buy vehicle insurance for the food truck, which they then used to have the truck towed back to L.A.

After the festival, Case's friend wrote an article on the truck for Curbed Los Angeles. The April 2009 post was one paragraph long: "Spotted at Coachella this weekend: Modern architecture-themed ice-cream sandwiches sold from a truck. No, we don't get it, either," it started. "The company, Coolhaus, will be hitting LA streets this summer and tweeting locations a la the more-famous-than-our-mayor Kogi Taco Truck," it read. "[The Curbed post] went viral. I do mean truly viral," says Case. "It's such a magic moment when that happens." With each new follower Coolhaus got on Twitter, Estreller got an email. Before Coachella, they maybe had 50, so every uptick was cause for celebration. The Monday after, Estreller called Case to say their account had been hacked. "'I've been getting like 5,000 emails,'" Case recalls Estreller saying. "And I was like, 'No, that's real. Like, this is really happening.'"

People were cheering for it to succeed because it's that hometown, cool story and it's relatable. Natasha Case co-founder, Coolhaus

Case thinks there are a few reasons the business took off. First, artisanal ice cream wasn't a thing yet, so it felt new. In fact, when they were first considering turning the quirky ice-cream sandwich hobby into a business, they Googled "hipster ice cream truck." There were no responses to the search query. Additionally, the economy was still in the Great Recession, so a budget-conscious food truck was appealing to consumers. Then there was their feel-good, underdog story. "Us being two young women taking the alternative path from our careers — it's the kind of thing that you do root for," says Case. Indeed, a recent CNBC/SurveyMonkey Small Business Survey of 2,030 small-business owners revealed that only 40 percent were women. According to the same survey, only 233 (11 percent) were under the age of 35.

Soon ice cream became Case's full-time job, when the company she worked for went out of business in 2009. Estreller kept her real estate job for two more years to allow the couple some financial stability. In the early days, Case's parents were not thrilled to see their daughter ditch architecture. "At first they had an intervention with me because — by the way, I would do the same thing; it came from love — they were like, 'You have this master's degree, and you're on this great path. Why are you buying an ice-cream truck?'" Case was among the most educated in that sense — only 18 percent of small-business owners have a post-graduate degree, according to the CNBC/SurveyMonkey Small Business Survey.

That's what it takes to be an entrepreneur. People are going to say, 'Are you sure?' And you have to be like, 'Yes.' Natasha Case co-founder, Coolhaus

But Case and Estreller never doubted their idea. Case told her parents, "We are going to laugh about this conversation in two years. I just have a feeling. This is the moment. We have to do this," she says. Her mom and dad did come around and have been very supportive, says Case. "But at first it was like, 'What the hell?' … That's what it takes to be an entrepreneur. People are going to say, 'Are you sure?' And you have to be like, 'Yes.'" It turns out Case and Estreller were right. Coolhaus now has 10 trucks: four in Los Angeles, four in Dallas and two in New York City. They opened a scoop shop in Culver City, Calif., and kiosks in Pasadena, Calif., and in the Dallas Farmers Market (the Texas location is a franchise). They've also expanded into selling wholesale and are currently in 6,000 retailers across the country from Whole Foods to Safeway. Revenue has also been climbing exponentially. In 2009, Case and Estreller made $100,000. "We thought we were rich. We couldn't believe it." The next year, they made $650,000. In 2011, they opened their first shop, got a first round of investment from an angel investor and cracked $1 million in sales.

In 2016, Coolhaus did $7 million in revenue and, this year, Case expects to do between $11 million and $12 million. The trucks and scoop shops bring in $2.5 million a year and the rest is from grocery stores. During the summer, Coolhaus has as many as 50 employees. Coolhaus recently raised $11 million in funding, which it will get over three years. The co-founders say the goal is for Coolhaus to be the Ben and Jerry's of this generation. Case thinks Coolhaus will be doing $25 million in sales in a couple of years. "We easily think it could be a $100 million brand." Now, Case, 33, and Estreller, 35, have married, have a young son and Estreller has left the day-to-day operations to start her own fun liquor brand — think gourmet Jello shots — called Ludlows Cocktails. Case says she is often asked to give advice to young entrepreneurs. She tells them not to wait for a product to be perfect before they go to market. And for women especially, she pushes them to dream big. Really big. "I think all the time, if my 25-year-old self were pitching me: 'We're going to do this architecture ice cream truck and we bought it…' I would be like, 'Whoa, whoa, whoa. Slow down. Do you even understand what you're getting into?' But I needed to be that 25-year-old who didn't really know much about it to just walk through all that. In a way, not knowing is an advantage." This article has been updated to correct information on Coolhaus' recent funding round. See also: How this mom turned $775 into a $65 million company in only 5 years How America's No. 1 small business got to $10 million brewing beer in Hawaii

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