Austere as this salad may seem, it's got 2 secret tricks that will make you better at making salads, during the holidays and forever after. 1. You infuse the vinegar with chopped red onion for an hour, then quietly remove it. The vinegar is left with a richer, more complex flavor, without the oppressive oniony kickback. 2. You toss the dressed leaves with a dusting of finely grated Manchego to help the coating stick. Adapted slightly from Toro Bravo: Stories. Recipes. No Bull. (McSweeney's Insatiables, 2013). —Genius Recipes
In a large bowl, add the balsamic vinegar, sherry vinegar, and chopped red onion. Break the onion up into pieces so that all of that oniony flavor gets into the vinegar. (Note: If you want to quick pickle and eat the onions themselves, Food52er hardlikearmour suggests adding the honey now too.) Let it sit for 1 hour and then strain out the onions.
Remove the cores from the radicchio and discard. Chop into 1-inch pieces. Take 1 gallon of water in a large bowl and add enough ice to make the water icy cold. Once cold, strain out the ice and add the radicchio to the water. Let it sit for 15 minutes to remove some of its bitterness, strain and then spin in a salad spinner until dry. Fluff the dried radicchio. (Note: If you don't strain the ice out before adding the radicchio you'll be pulling out ice pieces for half an hour so that you don't have wet radicchio.)
Add the honey and olive oil to the strained vinegars and whisk.
Using your hands, toss the radicchio with the dressing until evenly coated. Add 1 cup of finely grated Manchego, salt, and toss again.
To serve, top the salad in a serving bowl with the remaining 1/2 cup grated Manchego or distribute salad and Manchego among 4 to 8 bowls or plates.