Tip the flour into the bowl of a food processor, add the ground cinnamon, salt and the chilled, diced butter. Pulse until pale and sand-like in texture. Add the icing/confectioners’ sugar and mix to combine. Add the beaten egg and pulse again until the dough starts to come together.
Tip the dough out onto the work surface and use your hands to bring it together into a neat ball. Flatten into a disc, cover in clingfilm/plastic wrap and chill in the fridge for at least 1 hour until firm.
Roll out the chilled dough on a lightly floured work surface to a thickness of no more than 2 mm / 1/16 inch. Using the cookie cutter, stamp out 12 discs. Alternatively, as I don’t have a cookie cutter, I have just cut the dough in several pieces and then rolled it out one piece at the time.
Gently press the pastry discs into the prepared tart pans (just sprayed with a little bit of oil), trying not to stretch the dough until evenly lined. Prick the bases with a fork and arrange on a baking sheet and chill in the fridge for 20 minutes.
Preheat the oven at 170ºC (325ºF) Gas 3.
Line the tart cases with a square of baking parchment or foil and fill with baking beans or normal beans or rice. Bake in the preheated oven for 10 minutes until pale golden and starting to crisp. Remove the baking beans or rice and parchment foil, and bake for another 1-2 minutes to dry out the bases.
Roughly chop the hazelnuts and divide them between the tarts.
To make the filling, break the eggs into a mixing bowl, add the remaining ingredients, and whisk to combine.
Scoop the mixture into a jug/pitcher and pour into the tarts, filling them evenly. Top each filled tart with the hazelnuts and bake in the middle shelf of the oven for further 12-15 minutes until just set.
Remove from the oven and leave to cool to room temperature.
And now for the shiny part, warm the orange jam in a small pan until runny, strain into a bowl through a fine mesh sieve/strainer and brush neatly over the top of each tart. Leave to set before serving.