To brine pork: Toast fennel seed in a dry medium skillet over medium heat until fragrant, 2 to 3 minutes. Transfer to a mixing bowl. Add water, 1/4 cup salt and brown sugar, stirring until the salt and sugar are dissolved. Put pork in a large sealable plastic bag and add the brine. Refrigerate for 4 hours or up to 12 hours.

To prepare fennel: About 30 minutes before you cook the pork, position a rack in lower third of oven; preheat to 400 degrees F.

Cut each fennel bulb lengthwise into 6 wedges. Heat 1 tablespoon oil in a large skillet over medium heat. Add half the fennel wedges, cut-side down; sprinkle with 1/4 teaspoon each salt and pepper. Cook until golden brown, 4 to 5 minutes per side. Transfer the fennel to a medium roasting pan. Repeat with the remaining fennel, oil, salt and pepper. Transfer to the roasting pan and pour in stock. Roast for 20 minutes.

To prepare pork: Meanwhile, remove the pork from the brine. (Discard brine.) Pat dry. Combine vinegar, honey, mustard and fennel pollen in a small bowl.

Heat canola oil in the large skillet over medium-high heat. Add the pork and cook, turning often, until browned on all sides, about 8 minutes total.

Remove the fennel from the oven. Place the pork on top of it and brush with about half of the balsamic glaze. Return to the oven and roast until the fennel is tender and the pork registers 140 degrees F on an instant-read thermometer, 15 to 20 minutes.

Remove the pork to a clean cutting board and let rest for 10 minutes. Transfer the fennel to a serving platter; tent with foil to keep warm. Pour the liquid from the roasting pan into a small saucepan and add the remaining glaze. Bring to a boil and cook until reduced to about 1/2 cup, about 5 minutes.

Slice the pork 1/2 inch thick. Arrange on the platter with the fennel. Drizzle with the glaze and garnish with chopped fennel fronds, if desired.