Cook until the radicchio is deeply golden brown, about 1 minute.
Flip the radicchio over and allow it to brown on the other side, 1
minute, and then remove the radicchio to a plate.
Add the balsamic vinegar and chicken stock to the pan. Bring to
a boil and use a wooden spoon to dislodge the brown bits (those
have lots of flavor!), then return the radicchio to the pan, cut side
down.
Cover the pan and reduce the heat to low, allowing the liquid to
simmer and the radicchio to cook for 10 to 15 minutes until a knife
goes through it easily. If the liquid evaporates, add more chicken
stock.
To serve, carve the chicken and serve with the braised radicchio,
sprinkled with flaky sea salt, if desired. If you want, you can make
a sauce with the liquid left in the pan by bringing it to a boil,
adding the butter, and whisking until it’s nice and thick. Spoon
over the radicchio but not the chicken; you don’t want to lose the
delicate flavor of the fennel pollen oil. You can also serve the
chicken with spicy French mustard or bagna cauda, which is how
Dieterle serves his.
* Be aggressive. Use at least a tablespoon of salt for a 4-pound
bird.