Use a food processor to pulse the flour, butter, sugar and a pinch of salt until the mixture resembles breadcrumbs.
Tip into a bowl. Beat together one of the eggs and the milk then add this gradually and mix until you have a dough that comes together (about 1 tablespoon).
Knead the dough for a few seconds then divide into two, shape into rough rectangles, wrap in cling film.
Chill for 30 minutes.
Meanwhile, mix the cornflour with 1 tablespoon of cold water until dissolved.
Stir into the jam and set aside.
Remove the dough and roll both out on a lightly floured surface until there are two rectangles, roughly A4 in size.
Cut each sheet into 9 even sized rectangles.
Beat the remaining egg.
Line a baking tray with greaseproof paper and set aside.
Taking two rectangles in turn, brush one entirely with egg.
Spoon about 1 tablespoon of the mixture onto the other and sandwich together.
Transfer to the baking tray and use a fork to press the edges together.
Glaze with egg then prick with a skewer all over for the steam to escape.
Repeat then chill for 30 minutes uncovered.
Preheat the oven to 180°C / 350°F / Gas mark 4.
Remove from the fridge, glaze again with the eggg and cook for 18-22 minutes, until golden.
Allow to cool on a wire rack.
Make the icing sugar, almond extract (if using) and then add enough cold water, a drop at a time, until the icing is runny enough to paint onto the tarts.
Brush with the icing and then scatter with hundreds and thousands, sprinkles or whatever decoration, if you like.