Preheat oven to 350°. Spray a 9-inch round cake pan with baking spray with flour.
In a large bowl, beat ½ cup butter and granulated sugar with a mixer at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
In a medium bowl, whisk together Swans Down® Cake Flour, baking powder, and salt. Gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating just until combined after each addition.
In a medium microwave-safe bowl, melt remaining ¼ cup butter. Add brown sugar and corn syrup, stirring to combine. Arrange pecans in a single layer in bottom of prepared pan. Spread brown sugar mixture over pecans. Pour batter over brown sugar mixture.
Bake until a wooden pick inserted in center comes out clean, about 40 minutes. Let cool in pan for 5 minutes. Place a plate over pan, and invert cake onto plate.
Makes 1 (9-inch) cake