Surrounded by friends, family and rumored boyfriend Liam Hemsworth, the singer, who turns 17 Monday, let loose with an '80s themed bash last week at New York City's Canal Room.
"The whole thing was a surprise," says a source close to Cyrus, who enjoyed a performance by the cast of Broadway's Rock of Ages and blew out candles on a custom-designed cake created by Buddy Valastro, the star of TLC's Cake Boss.
"They didn't want a girly girl cake," says Valastro, who topped off the vanilla cake with Madonna-inspired lace, a stage and accents in Cyrus's favorite color, purple. "It totally fit the theme. It was really awesome."
It's a theme Cyrus knows all too well – when she turned 15, the singer also had an ‘80s themed party in her hometown, Nashville. "She loves the '80s," her mom Tish, who planned the Nov. 18 affair, told PEOPLE. "The fashion, the big hair– she thinks it's so funky."