Pulp the lemon in a food processor before adding the eggs, baking powder, bicarbonate of soda, almonds and sugar and processing until you have a smooth batter.
Grease a 20cm springform pan and preheat the oven to 180 Celsius (350 Fahrenheit).
Put the lemons in a saucepan with cold water and bring to the boil before reducing the heat and simmering for 2 hours, or until soft. Drain the water and set aside to cool. When cool, cut the lemons in half and remove any large seeds.