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.