Pre-heat oven to 375 degrees F (190 degrees C).
For Tart Shells:.
In a food processor, combine the flour, salt, and sugar. Add the butter and process until the mixture resembles coarse meal (about 15 seconds). Slowly pour 1/8 cup water in through the feed tube until the dough just holds together when pinched. If necessary, add more water to a maximum of 1/4 cup. Do not process more than 30 seconds.
Turn dough onto work surface and gather into a ball. Flatten into a disk, cover with plastic wrap, and refrigerate for about one hour.
After the dough has chilled sufficiently, roll out the dough and cut into 12 - 4 inch rounds. It may be easier to roll the dough between two pieces of plastic wrap, instead of on a floured surface. Gently place the rounds into a 12-cup muffin tin. You may need to coax the rounds into the tin, leaving a fluted edge. Place in the refrigerator for about 30 minutes to firm up.
While dough is chilling, toast and chop the pecans. Reserve 12 pecan halves, which will be used to top the tarts.
In a medium sized saucepan lightly whisk the eggs. Add the butter, sugar, and cream. Place on medium heat, bring this mixture just to a boil - stir constantly to prevent scorching. Immediately remove from heat and stir in the vanilla extract. (For a runnier filling, remove when filling starts to thicken but has not reached a boil.).
Place a teaspoon of chopped pecans into the bottom of each tart shell and then fill the unbaked shells with the filling. Top each tart with a whole pecan. Bake for about 15 - 20 minutes or until the pastry is nicely browned and filling is set.
Remove from oven and place on a wire rack to cool. Serve at room temperature or chilled.