John Mayer celebrated his 35th birthday yesterday over an intimate lunch with on-again love Katy Perry. The singers were spotted hiding behind dark sunglasses as they arrived at ABC Kitchen for a late lunch. A witness inside the Jean-Georges Vongerichten restaurant said the on/off/on couple looked romantic. The spy said, “It was hard to recognize them because Katy had a hat on that was covering her face. But she and John were alone, they were holding hands throughout the meal and they definitely looked like a full-on couple.” This comes after the two, who had appeared to cool off a little, spent a flirty Saturday night together. They were spotted at Hotel Chantelle on the Lower East Side, “kissing and partying together,” according to spies. Then they headed to Cabin Down Below for a more intimate rendezvous. According to a witness, “They were getting cozy in a small private room in the back.” Then on Sunday, they stepped out for a dinner date at Pearl Restaurant, smiling at the paparazzi. This is the latest relationship for the “Firework” singer since her divorce from Russell Brand was finalized. She had been linked to Florence + the Machine guitarist Robert Ackroyd and model Baptiste Giabiconi before dating Mayer.