Dont fry onions and garlic at the same time. Sweat the onions first and then add the garlic in the last 30 seconds before adding the other ingredients like broth or tomatoes. This will prevent your garlic from becoming bitter by overcooking.

Garlic becomes bitter? I had no idea and I eat the stuff by the bulb.

(To be fair, I don’t think oversteeped tea is bitter, either. And I think gin and tonic tastes sweet. So my sense of bitter might be a bit off.)