Preheat oven to 350°. Beat butter at medium speed with an electric mixer until creamy; gradually add sugar, beating 4 to 5 minutes or until light and fluffy. Add eggs, 1 at a time, beating until blended after each addition. Beat in lemon juice and vanilla.
Stir together flour and next 3 ingredients; add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat at low speed just until blended. Stir in strawberries.
Grease (with shortening) and flour a 13- x 9-inch pan; line with parchment paper, allowing 2 to 3 inches to extend over long sides. Lightly grease paper with cooking spray. Spread batter in prepared pan.
Bake at 350° for 30 to 40 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 30 minutes. Lift cake from pan, using parchment paper sides as handles. Invert cake onto wire rack; gently remove parchment paper. Cool completely (about 1 hour). Spread Strawberry Frosting on top and sides of cake.