Yep, just once. That was the challenge, though: make 13 attacks in a single round. The fighter can do it at 20th level, the sorcerer can do it at 12th, the wizard can do it at 10th.
But if you need to do it constantly for some reason, a 17th level sorcerer with eldritch blast (via the Magic Initiate feat) can still do it.
Action: 4 attacks with Eldritch Blast
Bonus action: 4 attacks with quickened Eldritch Blast.
Reaction: 4 attacks with Eldritch Blast (War Caster).
Haste: crossbow or whatever.
And if you're really into cheese, you can skip the Magic Initiate feat and get a two-level dip in warlock instead. Get that EB cantrip for free, and get the agonizing blast invocation to boot.
This character would annoy everyone at my table, and our DM would feed it to a beholder after the third combat scene and the rest of the party would help... but it can be done.