@JeremyECrawford @saintwinterer When did action surge gain the ability to ignore the one spell and one cantrip limit a turn?
— Derick Moore (@drgnlegend31) October 13, 2016
Is there a limit on the number of spells you can cast on a turn? See the Sage Advice Compendium for the answer: https://t.co/WWVq6Y8bNj #DnD https://t.co/5lfp4gAbrG
— Jeremy Crawford (@JeremyECrawford) October 13, 2016
Couldn’t find the answer in that massive wall of text.
That “massive wall of text” is no more difficult to read/understand than the PHB — it’s sectioned, listed, and addresses various questions beneath those listed sections. It should take a reasonable person no more than roughly 30 seconds to scan through the general headers then narrow down to the question (or close enough to it) that they’re looking for. Regardless, Jon’s response covers it for you/others.
There isn’t and never was a “one spell and one cantrip per turn” rule.
IF you cast a bonus action spell, THEN you can can only cast a cantrip with your action. If you don’t cast a bonus action spell, then that rule doesn’t say anything and there aren’t any restrictions.
So you can cast a spell using your action, counterspell a counterspell with your reaction, then action surge to cast another spell with your second action all without an issue. As long as you don’t cast a spell using your bonus action, you’re golden.
You can even cast a cantrip if you multiclassed enough to get Spare the dying fe as bonus action.
There are other ways to cast a cantrip as a bonus action, Quicken Spell metamagic, shillelagh, etc…
All of them count as casting a spell as a bonus action, which means the ONLY other spell(s) you can/could cast on that turn is a cantrip with a casting time of one action. So no, you can’t add a bonus action spell, even a cantrip, to other leveled spells in a turn.