To make the pastry, cut the butter into cubes.
Sift the flour in a large bowl, add the cubed butter, and use your fingertips to rub the flour and butter together until it resembles breadcrumbs.
Add the sugar and mix.
Crack in the egg, add the milk, and knead the dough gently until it's smooth.
Cover the dough with clingfilm and refrigerate for at least 30 minutes.
Flour the work surface, and use a rolling pin to roll the dough to a thickness of 3 mm.
Use a large cookie cutter (mine is 10cm in diameter) to cut out rounds - reuse the dough until you get 12 rounds.
Arrange the rounds onto the muffin tin holes and refrigerate the tin until the filling is ready.
To make the filling, melt the butter and transfer it to a bowl together with the sugar.
Mix them, add the egg beaten lightly, followed by the lemon juice, and mix again.
Add the walnuts and dried fruit, and mix to combine.
Divide the mixture evenly between each muffin tin and bake in the preheated oven at 180 degrees Celsius (350 Fahrenheit) for 25 minutes until the pastry is golden and the filling is set and risen.
Leave the tarts to cool down in the tin for 10 minutes, then carefully pop them out and leave them to cool down completely on a cooling rack.