Preheat oven to 350°F (175°C).

In a large bowl, combine white cake mix, strawberry Jell-O gelatin dessert, flour, water, oil, and eggs.

Add thawed frozen strawberries, reserving 3 tablespoons for the icing.

Mix all ingredients thoroughly until well combined.

Pour batter into a sheet cake pan.

Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cake cool completely.

To prepare the icing, in a separate bowl, cream softened butter.

Add 3 tablespoons of reserved strawberries and powdered sugar.

Mix all ingredients together well.

If the icing is too thick, add a little more juice from the thawed strawberries or water to achieve desired consistency.

Spread the icing evenly over the cooled cake.

Refrigerate for at least 30 minutes before serving.