Heat the oven to 180C/fan 160C/gas 4. Gently melt the butter, sugar and golden syrup together and stir in the oats, almonds and a pinch of the lemon zest. Tip the mixture into a 24 × 19cm buttered and lined tin. Pack the oat mix into the bottom of the tin using the back of a spoon. Bake for 30 minutes, or until the base is set and crisp. Take it out of the oven and leave to cool while you make the topping
Mix the lemon zest, eggs and sugar, then stir in the flour and finally the juice. Beat until smooth. Pour this carefully over the flapjack base and drop the raspberries all over it at intervals. Bake for a further 15 minutes, or until the top of the mixture has set, then cool completely before cutting into bars. Dust with icing sugar to serve.