Prepare pastry as directed and chill for 30 minutes. On a lightly floured surface (I use tapioca flour), roll out pastry to about 1/8” thick. Use a 4-inch round cutter to cut out 12 circles. Fit into muffin tin, chill for 30 minutes.
To prepare filling, whisk together brown sugar, maple syrup, butter, eggs, vinegar and salt.
Into each pastry shell, divide up any nuts, raisins or chocolate you wish to add, then top up with the filling. The filling won’t rise too much, so you can fill them close to the top.
Bake at 350°F for 20-25 minutes, or until filling is set and pastry is golden. Remove from oven and run thin knife around edges to release tarts if any filling has leaked out and stuck to the sides. Allow to cool in pan for 20 minutes, then transfer to rack to cool completely.