Preheat the oven to 160deg fan assisted. I used a steam oven.
Grease and line the bottom and sides of a 900g/2lb loaf tin with baking parchment.
Using an electric mixer, beat together the butter and sugar until light and fluffy.
Gradually add the eggs, adding a little of the flour to help prevent curdling. Mix until well combined.
Add the remaining flour, ground almonds, lemon juice and zest. Beat on low setting until well combined.
Pour the batter into the loaf tin and smooth the surface, then sprinkle the flaked almonds on top.
Bake in the oven for 1hr 10 mins or until baked. Testing the centre of the cake with a skewer until it comes out clean.
All ovens vary, so test your cake when 3/4 baked to give you an idea of how much longer you will need.
When baked, take out of the oven and leave in the tin to cool for about 10mins before turning out onto a wire rack to cool completely.
While the cake is cooling, place the sliced half lemon, water and sugar into a small pan and gently heat until the sugar has dissolved. Simmer for about 5 mins until the liquid turns syrupy. Decorate the cake with the sliced lemon and glaze with the residual syrup.
Will keep in an airtight container for a couple of days.