The day before you want to serve this dish, trim the sweetbreads of any fat and veins (or ask your butcher to do this for you). Put the sweetbreads
into a large bowl of ice water and refrigerate them for 24 hours, changing the water twice during this period. Drain
and rinse the sweetbreads well.
Put a rack in the lower third of the oven and preheat the oven to 350 degrees F.
Using a small paring knife, make a small hole in each sweetbread and push a fennel stick into it. Use half a fennel stick, if necessary.
In a spice grinder
, finely grind together the salt, fennel seeds, white peppercorns, fennel pollen, if using , saffron
, cayenne pepper
, and star anise
. Season the sweetbreads with this spice mixture and roll each one in the polenta
, coating all sides and shaking off any excess.
Warm the 2 tablespoons each olive oil and unsalted butter
in a medium cast-iron pot or Dutch oven
over medium-high heat. Add the coated sweetbreads, garlic, and fennel and sear
until the sweetbreads and fennel are light golden brown on all sides, 10 to 15 minutes. Deglaze
by adding the white wine and anise-flavored liqueur
, bringing to a boil, and scraping up any browned bits stuck to the bottom of the pot. Let simmer until the liquid is reduced by half, about 5 minutes.
Add the chicken stock and tomatoes, bring to a simmer
, transfer the pot to the oven, and braise
, uncovered, turning the sweetbreads once, until tender, 30 to 40 minutes.