Lightly butter 6x10 cm (4 inch) loose-bottomed fluted tart tins. Roll out pastry thinly on a surface lightly dusted with flour, arrange 5 tart tins on top, cut out the pastry a little larger than the tins then press into the tins and up the sides, trim the top of the pastry a little above the top of the tins. Reroll trimmings and make a 6th tart case. Prick the bases with a fork and chill for 15 minutes.
Preheat the oven to 190°C, 375°F, Gas Mark 5. Line the tart cases with pieces of nonstick baking paper and fill with baking beans or use dried macaroni or other small pasta shapes.
Bake for 10 minutes, carefully remove the paper and beans and cook the empty tarts for 5-6 minutes until just beginning to brown around the edges.
To make the filling, beat the butter and sugar together until light and fluffy, gradually beat in the eggs then stir in the ground almonds and almond essence. Divide between the tart cases, spread into an even layer then sprinkle with the blueberries and flaked almonds.
Bake at 180°C, 350°F, Gas Mark 4 for 20-25 minutes until golden.
Leave to cool for 20 minutes or until ready to serve. Remove from the tart tins and dust with sifted icing sugar, if liked. Serve with spoonfuls of crème fraîche.