Place sliced leek in a colander; rinse and drain well.

Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Season chicken with 1/4 teaspoon salt and 1/4 teaspoon pepper and cook until golden brown and no longer pink in the center, 4 to 5 minutes per side. Transfer to a plate and tent with foil to keep warm.

Reduce heat to medium and add the remaining 2 teaspoons oil to the pan. Add the leek and cook, stirring, until beginning to brown and soften, about 2 minutes. Add pear and 1/4 cup broth; simmer until the pear is soft and the broth is evaporated, about 2 minutes.

Meanwhile, whisk the remaining 1/2 cup broth and cornstarch in a small bowl. Add currant jelly to the pan and cook, stirring, until melted. Stir in the cornstarch mixture, the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Bring to a boil, stirring, and cook until thickened, about 1 minute. Return the chicken and any accumulated juices to the pan and turn to coat with sauce. Serve sprinkled with walnuts.

Tip: You'll need about 1 1/2 pounds untrimmed boneless, skinless chicken thighs to serve four people. For recipes that call for one large thigh per person, buy them at the butcher counter; prepackaged thighs vary dramatically in size. Ask for four 6-ounce boneless, skinless thighs. To trim them well, we like to use kitchen shears to snip the fat away from the meat. After trimming, you'll have four 4-ounce portions.

Tip: Toast walnuts in a small dry skillet over medium-low heat, stirring constantly, until fragrant and lightly browned, 2 to 4 minutes.