Prepare tart shell. Combine flour and butter in food processor. Process until it reaches the fine crumb stage. Add one egg and process until dough forms a ball. Press evenly into bottom and sides of a 9 inch spring. Bake for 20 minutes on the middle oven shelf. Crust will be firm to touch but not brown.
Thinly slice and lightly sprinkle tomatoes with kosher salt. Allow to drain in colander for 15 minutes or more. Place cheese in tart shell. Top with tomato slices and sprinkle with chives and basil.
Wisk together 3 eggs, half and half, mustard, salt and pepper and baking powder. Pour into shell. Bake at 350 degrees for 25 to 35 minutes until custard is firm. Allow to cool for 10 minutes.