Preheat oven to 375 degrees. Season grouper with salt and white pepper 20 minutes before cooking. In a mixing bowl, slice tomatoes in wedges and season with salt and finishing oil only – no pepper.
Peel mango and slice lengthwise around pit. Slice long strips in thin slices and set aside.
For blackberry sauce, combine blackberries and a little water in blender. Blend and strain through a fine mesh strainer. In a small saucepan, combine sugar and balsamic vinegar and cook until it starts to thicken. Do not over-reduce or will be too thick once it cools. Set aside. Heat. cup of grapeseed oil in a saute pan until it comes to a smoking point. Place only two seasoned grouper filets in the pan at a time. Cook for about two minutes on one side, until golden brown. Then turn the fish in the same pan and place in the oven to finish. It should take 8–10 minutes longer in the oven. Your cooking time can vary depending on how your grouper is cut. Once grouper is out of the oven take out of the pan and let them rest. Repeat with other filets.
To plate: Starting with blackberry sauce, paint your plates, add tomatoes and mango and filet. Garnish with basil and fleur de sel lightly dusted on the dish.