Add the flour and salt in a food processor and process until blended. Add the butter and pulse until you get the crumbly mixture. Add the shortening and pulse few more times.

In a small bowl, whisk together the egg, vinegar, and 2 tablespoons of really cold water. Pour this mixture into the food processor while it's running and process until the dough starts forming.

Transfer the dough to a lightly floured surface. Gather it together and form it into a disk. Wrap in plastic wrap and refrigerate for 30 minutes minimum.

In a saucepan, over medium-high heat, combine the butter, sugar, and heavy cream.Stir until the butter is melted, and the sugar is dissolved. Remove from heat and let cool for few minutes. Whisk in the egg, bourbon (if using), salt, and add the pecans.

Preheat the oven to 400°F (200°C).

Take the dough from the fridge and roll it out on a floured surface to ⅛ inch thick. Cut the dough to 4-inch circles. You should get about 12 circles. Now press down each one of them into the wells of a 12-well muffin tin. Fill them with the filling until they are about ¾ full.

Bake the tarts for 10-15 minutes, until golden. Let them cool for 5 minutes, then use the knife to loosen sides and remove them from the tin. Enjoy!