Remove roots, outer leaves, and tops from leeks. Rinse under cold water; cut into 1 1/2 x 1/2-inch strips.
Combine leeks, lemon juice, olive oil, 1/4 teaspoon salt, and pepper in an 11 x 7-inch baking dish. Bake at 500° for 20 minutes or until leeks are tender, stirring once. Spoon leek mixture into a bowl; set aside. Reduce oven temperature to 350°.
Coat baking dish with cooking spray, and arrange half of the potato slices in dish. Spread leek mixture over potato slices. Top with remaining potato slices; sprinkle with 1/4 teaspoon salt.
Combine the milk and Spiced Pear Butter in a small bowl, stirring with a whisk until smooth; pour over potato slices. Cover loosely with foil; bake at 350° for 45 minutes. Uncover and bake 30 minutes. Sprinkle with cheese, and bake an additional 10 minutes.