Floyd Mayweather even balls out on CAKE ... 'cause his birthday dessert was covered in crystals and cost $3,000 ... TMZ Sports has learned.
We spoke with the maestro behind the insane dessert, Bree Miller -- who says she spent 72 hours on the 6-tier cake.
Plus, Miller says she strung 12 feet of Swarovski crystals around the masterpiece ... because she knew Floyd's cake needed that Money Team swag.
Oh ... and yeah, we're told it tasted DELICIOUS!!!