In a mixing bowl, add the cornmeal, flour, salt and butter. Using two knives or your hands, mix the butter into the flour mixture until it reaches a sand-like texture. Add the sour cream and then the water and mix until you have a smooth dough. Wrap in plastic wrap and refrigerate for 1 hour.
Preheat oven to 400 degrees.
In a mixing bowl, add the cream cheese, cheddar and Parmesan. Set aside.
Heat a medium skillet over medium heat and add the oil. Saute the onion and fennel until soft, 5 to 7 minutes, then transfer into the bowl with the cheese. Cover and allow cheese to melt.
Spread the sliced tomatoes on a cutting board and sprinkle with salt. Set aside.
Remove dough from the refrigerator and roll out on a floured surface until about 1/4 inch thick. Place on a parchment lined sheet tray and spread cheese mixture over the top, leaving a 1 1/2-inch border.
Blot tomatoes with paper towels to remove excess liquid and place on top of cheese in a circular pattern. Fold the edges of the dough over, and brush with egg wash. Bake for 30 to 40 minutes, until the crust is golden brown. Serve sprinkled with torn basil.