For the dough: Combine flour, sugar, baking powder and salt in a food processor fitted with metal blade. Pulse several times to mix. Add butter and pulse about 15 to 20 times to reduce mixture to a fine powder. Add eggs and pulse again, continuing to pulse until dough forms a ball. Remove dough from work bowl, wrap and chill. Preheat oven to 325 degrees and set rack in the lowest position. Butter a 9-inch layer pan, 2 inches deep. Roll the dough about 1/4-inch thick and line the pan. In rolling, keep the dough as close as possible to the size of the pan.
For the filling: Whisk sugar and flour together in a mixing bowl, then wisk in eggs, 2 at a time. Whisk in remaining ingredients one at a time. Pour filling into prepared pan and bake for 1 hour, or until the filling is set and the crust is golden. Cool pan and refrigerate covered.
To unmold, warm bottom of pan and invert tart onto plate or cardboard. Remove pan and replace with another plate or cardboard. Reverse again. Serve very cold.