Preheat oven to 350°.
Coat a 13- x 9-inch baking pan with cooking spray, and dust with 1 teaspoon cake flour; set aside.
Combine cocoa and chocolate in a small bowl; add boiling water, stirring until chocolate melts. Set aside.
Combine sugar, butter, and oil in a large bowl; beat at medium speed of a mixer about 2 minutes or until well blended. Add vanilla and eggs; beat well.
Combine 2 1/4 cups cake flour and next 3 ingredients. Add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat in chocolate mixture.
Pour batter into prepared pan. Bake at 350° for 30 to 32 minutes or until a wooden pick inserted in center comes out clean.
Let cool completely in pan on a wire rack. Spread Mocha Glaze over cooled cake.
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