Billionaire philanthropist Bill Gates has come up with a creative way to wish his friend Warren Buffett on his 90th birthday. "Happy 90th birthday, Warren!" the tweet said, accompanied with a minute-long video that shows Gates donning an apron and baking a special Oreo cake bearing Buffett's face. Gates also shared a tribute for his friend on his blog 'GatesNotes'. "Warren Buffett turns 90 years old today. It’s hard to believe that my close friend is entering his tenth decade. Warren has the mental sharpness of a 30-year-old, the mischievous laugh of a 10-year-old, and the diet of a 6-year-old," the Microsoft co-founder wrote. Watch the video here: Happy 90th birthday, Warren! pic.twitter.com/8nH2EulTR4 — Bill Gates (@BillGates) August 30, 2020 In the blog, Gates reminisced about the good times the duo shared together. "I couldn’t possibly list all the interests Warren and I share. But one thing we discovered the first time we met is that we both love math and numbers." The video concludes with the cake being layered with one of Buffett's "favourite cookies", as mentioned by Gates and featuring the American investor's face.