1. Crush the fennel seeds with mortar and pestle or with the side of chefs knife against a cutting board. Combine the flour, crushed fennel seeds and salt in food processor. Whirl for 3 seconds. Add the butter. Pulse until the mixture resembles coarse crumbs. With machine running, add water, tablespoon at a time, until dough just starts to come together; do not overprocess. Gather dough into ball; pat into 8-inch disk. Cover with waxed paper. Chill until firm, about 40 minutes.
2. Heat oven to 400 degree F.
3. On a lightly floured surface, roll dough into a 14-inch round. Carefully lift dough into a 12-inch tart pan with removable bottom; ease dough gently into the pan, being careful not to stretch it. Trim edges. Prick dough in bottom of pan (not side) all over with fork. Line dough with aluminum foil, gently pushing foil against side of tart pan to prevent shrinkage. Fill foil with dried beans or pie weights.
4. Bake crust in 400 degree F oven on bottom rack for 15 minutes.
5. Remove pastry shell from oven. Carefully remove foil and beans or weights. Brush bottom of shell with egg white. Return tart shell to oven and bake for another 10 minutes or until golden. Remove tart pan to wire rack to cool slightly.Meanwhile, prepare Tomato Filling:
6. Combine the olives, shallots, thyme and olive oil in small bowl until blended. Sprinkle the cheese over the bottom of the cooled pastry shell. Arrange the well-drained tomato slices in concentric circles over the bottom of the tart. Sprinkle tomatoes evenly with the salt and pepper. Spoon olive mixture over top of tomatoes.
7. Bake tart in 400 degree F oven for 20 to 25 minutes or until the cheese is melted and tomatoes are golden and bubbly. Transfer the tart to a wire rack to cool slightly before serving. Garnish with thyme sprigs.