Combine dry ingredients for crust in a bowl. Cream in softened butter.
Beat egg with vanilla and salt, and blend into batter. Form into shallow eight-inch straight-sided tart pan (a pie pan also works, but not as well).
Cover the tart dough with aluminum foil and fill with about a half-cut of dry red beans or pie weights. Place crust in preheated oven and bake with beans for 10 minutes. (This keeps sides from caving in, and the bottom from bubbling up.) Remove foil and beans and bake another five minutes. Cool crust. Reduce oven heat to 325 degrees.
Start the filling by beating the eggs. Blend in sugar slowly. Stir in juice, followed by lemon zest.
In a saucepan, melt the butter but don't let it get hot. Stir the butter into the egg-lemon mixture.
Pour the filling (it will be very liquid) into the tart shell, and put it in the center of the 325-degree oven. Bake 20 minutes. Allow to cool. Serve with garnish of fresh raspberries or strawberries.
