Grease a 10" X 14" sheet cake pan.

Whisk together the flour, cornstarch, baking powder, and salt.

On medium-high speed, cream together the butter, sugar, and vanilla.

Add the eggs and mix thoroughly.

Reduce the mixer speed to low. Slowly add the dry ingredients until incorporated completely.

Preheat the oven to 400 degrees F.

The cake batter will be the consistency of cookie dough. Spread it out on the greased sheet cake pan. To make this easier and to distribute the batter evenly into the pan, wet the back of a rubber spatula with water to smooth out the batter. Wet your hands as well if you are using them to help even out the mixture.

Starting at the shorter end of the pan, use a ruler to measure out the space across, dividing the section into 4 equal squares, 2+1/2 inches square each.

Mark the squares by dragging a toothpick through the top of the batter.

Repeat underneath to create another row of the same-sized squares below this first one.

Repeat until the entire pan of cake batter has been scored into squares.

Working with one type of fruit at a time, place each type in its own square.

Gently push the fruit into the batter, alternating fruit varieties.

Bake for 40 minutes until the cake becomes golden brown.

Let cool completely before cutting and serving.