Preheat oven to 350 degrees.
Cream butter and sugar at medium speed with an electric mixer until fluffy and pale in color – about 3-4 min.
Add eggs, 1 at a time, beating for a few seconds between eggs.
Beat in vanilla and lemon juice.
In a separate bowl, stir together cake flour, strawberry flavored gelatin, baking soda and salt.
Add flour mixture to creamed butter mixture and alternate with buttermilk, ending with flour mixture.
Blend on low speed until incorporated.
Fold in diced strawberries.
Grease and flour a 9x13-inch baking pan and line with parchment paper.
Allow a couple of inches of parchment paper to drop over the edges of the pan. Spray parchment with cooking spray and pour batter into prepared pan.
Smooth batter evenly.
Bake at 350 degrees for 30 to 35 min or until toothpick inserted in center comes out clean.
Cool in pan on a wire rack 30 min.
Using flaps of parchment paper as handles lift cake from pan.
Turn cake over onto wire rack and cool completely.