Heat the oven to 180C/160C fan/gas 4. Butter a 20cm round cake tin and line with baking parchment. Beat the butter and sugar together for 5 mins until pale and fluffy. Mix in the lemon zest, then add in the eggs, one at a time, beating well after each addition. Stir in the almond extract. The mixture may look split at this stage, but it will come together once the flour is added.

Tip in the ground almonds and flour, and mix to combine. Scrape into the prepared tin. Scatter over the flaked almonds and bake for 40-45 mins until golden and a skewer inserted into the centre comes out clean. Leave to cool completely in the tin, then dust over the icing sugar to serve.