1. First make the 'mincemeat'. Put the prunes, figs, port and mixed spice into a small saucepan and bring to a boil. Reduce the heat to a simmer and cook down until the port has been almost entirely absorbed into the fruits - you should be left with somewhat of a mush. Remove from the heat and allow to cool a little.
2. Roll the pastry out to a thickness of about 4mm (though Christmas really isn't the time for precision). Cut out discs big enough to line the cavities of the mini muffin tin (I find a 6cm cookie cutter gives the right size). Chill the tin until required.
3. Preheat the oven to 170C fan/190C conventional/gas mark 5.
Cream together the sugar and butter until the sugar has more or less dissolved into the butter, and everything is paler in colour and lighter in texture. Throw in the egg and almonds and beat to a smooth batter. Mix the cooled fruit mixture into the almond mixture, then spoon or pipe it into the pastry-lined mini muffin tin - the mixture should just come to about 2mm from the edge of the pastry.
4. Bake the tarts for 20-25 minutes, until the pastry is golden and the frangipane is dark and has puffed up. Remove from the oven, tip the pies out of the muffin tin, and set them onto a wire wrack to cool completely.
5. For the buttercream, beat the butter until soft - I use a handheld electric mixer. Add the sugar and beat in gently to avoid a cloud of icing sugar smoke, then beat until very pale. Add the cream cheese and St Agur, and beat to a smooth buttercream - don't over-beat it. Load the buttercream into the piping bag, and pipe a blob onto each pie.