1. Preheat oven to 350°. Grease (with shortening) and flour a 13- x 9-inch pan. Pour 1 1/2 cups boiling water over tea bags in a heatproof glass bowl. Cover with plastic wrap, and steep 10 minutes. Lift tea bags from liquid, and press against side of bowl, using back of a spoon; discard tea bags. Cool tea 20 minutes.
2. Beat butter in a separate large bowl at medium speed with an electric mixer until creamy. Gradually add sugars, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition. Whisk together cake flour and next 3 ingredients; add to butter mixture alternately with 1 cup tea, beginning and ending with flour mixture. (Discard any remaining tea.) Beat at low speed just until blended after each addition. Pour batter into prepared pan.
3. Bake at 350° for 35 to 40 minutes or until wooden pick inserted in center comes out clean. Cool completely on a wire rack (about 20 minutes). Spread Lemonade Frosting on cake.
Note: We tested with Luzianne Iced Tea tea bags.