In a large bowl, combine flour with salt. 

Cut in butter and shortening with a pastry blender until mixture resembles coarse meal (there should be some larger pieces). 

In a liquid measuring cup, whisk egg yolk with teaspoon of vinegar. Add water until it reaches 1/3 cup mark. 

Gradually add to flour mixture, stirring briskly with a fork until pasty holds together. 

Gather dough into a ball, flatten into a disc and wrap in plastic wrap. Refrigerate at least one hour and up to three days.

In a medium bowl, whisk together well the brown sugar, corn syrup, egg, butter, vanilla, vinegar and salt.

Roll out pastry to 1/8 inch thickness. 

Using a 4″ cookie cutter (or 4″ wide glass) cut out 12 circles. Reroll dough if necessary.

Place dough into muffin tray for 12. Spoon filling until three-quarters full.

Bake in bottom third of oven at 450F for about 12 minutes or until filling is puffed and bubbly and crust is golden. 

Let stand on cooling rack for one minute.

Quickly run a knife around tarts to loose and transfer to rack to cool.