Coat bottom of a 9-inch round cake pan with melted butter. Sprinkle with brown sugar, and arrange pear slices over sugar in an overlapping pattern.
Beat 1/4 cup butter at medium speed of an electric mixer until creamy; gradually add 2/3 cup granulated sugar, beating well. Add egg and banana, beating well.
Combine flour, soda, and salt in a small bowl; add to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Mix at low speed after each addition until blended. Spoon batter over pear slices.
Bake at 350° for 30 to 35 minutes or until a wooden pick inserted in center comes out clean. Cool 5 minutes in pan on a wire rack. Loosen cake from sides of pan with a narrow metal spatula and invert onto a cake plate. Serve warm.