For the dough: Combine the flour, butter and some salt and pepper using a pastry blender or 2 knives until the mixture resembles coarse meal. Mix in 2 tablespoons of the oil and the water just until the bottom of the mixture begins to cling together. If necessary, add an additional tablespoon of oil. Gather the dough into a ball and flatten into a disk. Wrap the disk in plastic wrap and chill for 30 minutes.
For the tart: Preheat the oven to 375 degrees F. Roll the chilled dough into a 14-inch circle and place into a 12-inch tart pan with a removable bottom. Chill in the refrigerator for 15 minutes.
Spread the mustard over the bottom of the tart shell. Sprinkle the Gruyere evenly over the mustard and alternately place the tomato and Camembert over the Gruyere. Bake on the middle shelf of the oven for 35 minutes.
Mix together the olive oil, basil, parsley, thyme and garlic in a small bowl. Brush two-thirds of the mixture over the tart. Remove the tart and cool briefly before serving. Serve warm with the remaining herb oil.