Place the lemons in a medium saucepan and cover with water. Bring the water to boil and then reduce to a simmer. cook the lemons for about 1- 1,5 hours, until the lemons are soft and a spoon goes through the skin very easily. Once soft, place in a bowl and let them cool down.
Preheat the oven to 190 degrees C. Grease the cake tin, about 20 cm.
Mix the lemons in a food processor until you have a fine purée. Remove any seeds that remain. Add sugar, almond meal, eggs and baking powder. Mix again until well combined. Pour the batter into the cake tin and bake for about 1 hours. Insert a metal skewer in the middle of the cake and when it comes out clean, the cake is ready.