In a bowl or food processor, combine flour, sugar replacement and margarine.
With a steel blade or knife work into a mixture like cornmeal.
Add vanilla extract and enough water to make a soft dough.
Press dough evenly into a 9 inch (23 cm) false-bottom tart pan.
Chill in refrigerator for 45 minutes.
Cover the chilled dough with aluminum foil and fill with dried beans or pie weights.
Bake in the lower part of a 400°F (200°C) oven for 8 minutes.
Remove foil and beans and bake the crust for 5 minutes longer.
Remove from oven.
Combine filling ingredients and beat well.
Pour into partially baked shell.
Set on the middle rack of the oven and bake for 20 to 30 minutes, until filling is set and a knife inserted in center comes out clean.
Cool before serving.