Rinse the leeks well and separate the layers to ensure no dirt remains. Slice into 1/4-inch thick half moons.

Preheat the oven to 375 degrees F.

Mix 1 1/4 teaspoons salt, 1/4 teaspoon pepper, and paprika. Season all sides of the chicken thighs with this mixture.

Heat a large oven-safe skillet or Dutch oven on high heat. Add a spray of olive oil and brown the chicken thighs on all sides, about 5 minutes each, adjusting heat as needed.

Set browned chicken aside and repeat with remaining pieces if necessary.

Reduce heat to medium-low. Add butter to the skillet. Once melted, add sliced leeks and sauté until soft, about 6-8 minutes. Add mushrooms, sprinkle with 1/4 teaspoon salt, and cook covered for 5 minutes, stirring to release juices.

Sprinkle flour over the vegetables, stir in chicken broth and sherry. Simmer for 2-3 minutes.

Return the chicken to the skillet, spoon the sauce over it. Cover and bake in the preheated oven for 40-50 minutes until cooked through and tender.