Pre-heat the oven to 200°C.
Roll the pastry out on a lightly floured work surface to ½cm thickness. Use a 12cm circular cookie cutter to cut out 4 rounds of pastry (use a sharp knife and a small inverted saucer if you don't have a cutter). Carefully lift onto a lined baking tray and prick them all over with a fork.
Sprinkle the ground almonds onto the base of the pastry, covering evenly. Arrange the slices of apple on top, overlapping in a concentric circle, leaving a 2-3cm border at the edge of the pastry. Sprinkle the brown sugar on top, then dot the surfaces with the butter.
Bake for 15-20 minutes until the pastry is risen and the apple is soft. Remove and let them rest for 1-2 minutes on the tray.
Meanwhile, heat a small frying pan over a moderate heat and toast the flaked almonds, tossing occasionally, for 1 minute. Arrange the tarts on serving plates and sprinkle the flaked almonds on top.
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