To prepare cake, combine first 5 ingredients, stirring well with a whisk.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking soda, 1/4 cup pecans, and 1/2 teaspoon salt in a large bowl, stirring with a whisk. Add syrup mixture to flour mixture; stir until well blended. Pour batter into a 9-inch square baking pan coated with cooking spray. Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool completely on wire rack.
To prepare frosting, combine sugar, 2 1/2 tablespoons syrup, cream, and 1/8 teaspoon salt. Beat with a mixer at medium speed until smooth. Spread frosting evenly over cooled cake; sprinkle with 1/4 cup pecans.