It all went down Wednesday night at Gloria Estefan's waterfront mansion on Star Island in Miami ... where J Lo's famous friends like DJ Khaled, Fat Joe, Ryan Seacrest and Ashanti rolled to party with Jenny from the Block.

43-year-old A-Rod gifted Jennifer a sick red Porsche 911 GTS convertible, worth around $140,000!!!

He also gave a big speech in front of the crowd, telling Jennifer that he loves her deeply and is so happy to be a part of her 50th birthday. It was sweet.

And, speaking of sweet, the cake was lit too! It was 10 TIERS and it was taller than most of the guests and took 5 grown-ass dudes to carry it into the party!

We're also told it was covered with with 24-karat edible gold and featured her name and the number “50” in Swarovski crystals. And, it was delicious too -- a Divine Delicacies Custom vanilla rum cake with dulce de leche filling. The bakery had no comment.

We're told the total cake cost -- $10,000!!!

As for the party itself, everyone was turning up ... even her kids hopped onstage and serenaded J Lo with a birthday rap song. It was adorable!

Also, Fat Joe bumped his hit, "All the Way Up" ... and the place went NUTS!!!

Lopez was also gifted a huge portrait of herself that was also bigger than most of the guests!!

The big grand finale was an explosive fireworks display over the water -- it was like the 4th of July all over again!!!

By the way, Jennifer isn't taking too much time to recover ... she's got a concert in Miami on Thursday, Friday and Saturday night, which will close out her tour.

Props to A-Rod for setting the whole thing up and everyone seemed to have a blast -- and now, we're all thinking the same thing in the office ... how are they gonna one-up this party for the wedding bash?!!