Reducing a tomato based sauce brings out deep “Basso profundo” flavors but diminishes the brighter, fresher notes of the tomato. Reserving a portion of the sauce un-reduced to return near the end restores the “treble” flavors back into the mix.
I discovered this trick accidentally when making sauce for two large lasagnas using a too-small pot. I was forced to set some aside. Rather than waste it I figured why not add it at the end. The result was a thrilling surprise. Returning the lightly cooked sauce near the end restored the bright flavors without masking the deeper ones. It’s like turning up both the bass and the treble on your stereo, thus the “Equalizer”.
Make a big batch! A couple of days in the fridge or a few months in the freezer will do the sauce no harm at all.