Preheat the oven to thermostat 7 (210°C).
Generously butter a 26 cm pie dish and line it with the pastry. Prick the base with a fork, then sprinkle evenly with ground almonds mixed with 50 g caster sugar and the cinnamon. Bake for 10 minutes to set the base.
Halve the quetsches and mirabelle plums, remove the pits, and arrange them cut-side up on the pre-baked pastry. Sprinkle with the remaining 30 g caster sugar, drizzle over the plum brandy, and return to the oven for 20 minutes until the fruit is tender and caramelized.
Allow the tart to cool completely before unmolding. Dust with icing sugar just before serving.
Pair with whipped heavy cream or Chantilly, subtly infused with aged plum brandy for an authentic touch.
