Photo by Sam Neill

When Florence and the Machine, closes out the Austin City Limits Music Festival on Sunday night, singer Florence Welch will front an 11-piece ensemble. Guitar, bass, keys, piano, a three-piece horn section, two backup singers and a harpist will all weave harmonies into the ornate tapestries of her majestic baroque rock. Rolling Stone magazine crowned the band “Best of the Fest” at Lollapalooza earlier this year.

But the first time she played Austin as a 21-year-old art school dropout, it was a stripped down set at South by Southwest with guitarist Rob Ackroyd. They played at Rio Grande Mexican Restaurant, a converted warehouse that once hosted the “Real World Austin” and now houses Vince Young’s Steakhouse over a year before their debut album “Lungs” was released. There was a fountain in the club and by the conclusion of the set, she had doused herself and a friend in it. She ended her set by diving under the stage.

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From her home in London, Welch laughs about the memory. “Someone was yelling like, ‘There’s rabies in the pool!’ And then they were yelling at me like, ‘Don’t go underneath the stage, that’s where all the electricity is!’ And so basically, it was like everywhere was like a death trap,” she says.

Like many young bands, Welch’s first SXSW involved a lot of running around “pretty drunk and excited.” She caught some great shows — Bon Iver was amazing. She went to the Black Cat downtown and randomly selected her first tattoo, a heart draped with a banner carried by a blue bird that reads “sad sack.” It was all very typical, except her experience was also the stuff SXSW dreams are made of. That delirious set on a makeshift stage at a Mexican restaurant would launch her career. Welch and Ackroyd were followed by electro-psych rockers MGMT, one of the year’s big breakout acts.

“From that gig they gave us their support slot across Europe and England, which, actually … that really kind of broke us,” Welch says.

Here she is debuting the song “Between Two Lungs” at that gig.

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And here she is playing the song “Delilah” at Glastonbury earlier this year.

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Our full interview with Welch is coming later this week.