In a large bowl mash together garlic cloves, fennel seed, salt. Stir in pepper, and 1/2 tablespoon oil. Rub the mixture over pork strips, pressing in well. Heat a large skillet over medium-high heat. Add the pork and cook until lightly browned on each side, about 1 1/2 minutes on each side. Transfer to the oven and roast about 20 minutes, or until the internal temperature reaches 150°F (65°C).
Meanwhile, heat 1/2 tablespoon oil in a heavy saucepan over medium-low heat. Add chopped leeks and chopped onion; cook, stirring often, until softened, about 3 to 5 minutes. Add chicken broth and bring to a simmer. Cover and cook until the vegetables are tender, about 10 to 15 minutes. Transfer to a food processor and blend until smooth. Return to the saucepan and keep warm.
Remove the pork from the baking pan and set aside, keeping meat warm. Add white wine to pan and cook, stirring until well blended with the pan drippings and reduced by half. Add to the fennel mixture with sour cream. Serve the sauce with the sliced pork.