Move oven rack to middle position and preheat oven to 350 degrees F. Prepare water bath by filling 9-13-inch metal baking pan a third of the way full with water, and set aside.
Lightly grease 8x8-inch baking pan with nonstick cooking spray, and set aside.
In large bowl use handheld mixer on medium speed to beat butter until creamy and lightened in color, about 1-2 minutes. Add masa harina and water and beat on low speed until combined, about 1 minute.
Using food processor or blender, chop corn by pulsing 3-5 times. Corn should be chopped but still chunky. Stir corn into butter mixture until combined, and set aside.
In medium bowl combine cornmeal, sugar, cream, salt, and baking powder. Add to butter and corn mixture and stir with wooden spoon until cohesive batter forms. Pour into prepared 8×8-inch baking pan, smooth into even layer, and cover with aluminum foil. Place pan into water bath.
Bake for 50-60 minutes, or until completely set, rotating pan once while baking.
Move to wire rack and cool for 15 minutes. Use small ice cream or cookie scoop to scoop sweet corn cake mounds onto plates for serving.