Mix eggs with the sugar substitute, then stir in the syrup, melted butter, and vanilla.
Lay the pie crusts flat and find a glass or bowl about an inch in diameter wider than the cups of your muffin tin. Use the glass/bowl to cut out as many tartlets as you can, rolling up and flattening any excess to cut more.
Place the tartlet rounds in the muffin cups, letting the rounds come up the inside of the cup about a half inch. Use a large spoon or a measuring cup to scoop the filling into the tartlet cups. Sprinkle pecan halves onto the filling in the tartlets.
Bake for 25 to 30 minutes or til the pastry is golden brown. Using the tip of a small knife, gently lift the tartlets from the pan and set them on a wire rack to cool for about 10 minutes.
You can fill and bake the tartlets up to four weeks ahead and freeze them. Put the cooled tartlets on a shallow pan and freeze until firm, then layer them between waxed paper in an airtight container. Baked tartlets will also hold for three days in the fridge, wrapped in waxed paper and then foil (not plastic wrap). To refresh, bake the tartlets at 325°F for 5 to 7 minutes if refrigerated or 12 to 15 minutes if frozen.
