Put the butter, sugar, flour and baking powder in a large bowl. Break in the eggs, add the almond essence, if using, then beat with an electric mixer until smooth and creamy. Set aside a quarter of the mixture, then stir the chopped apricots and 25g of the biscuits into the remainder. Spoon into the tin and lightly smooth with the back of the spoon. Bake for 25 mins until the cake is almost set. Meanwhile, stir the apricot halves, remaining biscuits and flaked almonds into the reserved cake mixture until well mixed. Quickly dot the extra cake mixture onto the part-baked cake, then return to the oven for 20 mins more or until a skewer inserted into the centre of the cake comes out clean.