Roll out pastry to line a 23 cm/9” flan ring or case and chill in the fridge for 10-15 mins. Then place baking or greaseproof paper on top, fill with baking beans and blind bake for 12-15 minutes.
Meanwhile combine the butter, sugar and almonds and then beat in the eggs and vanilla essence.
Once the pastry is just cooked but not too brown, remove from the oven, spread base with jam and allow to cool for 5 minutes. Meanwhile lower oven temperature to 190ºC (170ºC fan assisted oven)/Gas 5.
Then spread almond mixture evenly over the jam and scatter over the slivered almonds. Return to oven and bake for 25-30 minutes until the filling is golden brown and set in the middle. You can tell this by gently shaking the tin. If the filling appears to ‘wobble’, then return to oven. If the top is getting too brown then lower temperature by a further 10ºC.