Pre-heat the oven to 180C. Line the bottom of a 9-inch round cake tin with baking paper, and lightly grease the bottom and sides.
Cream together the butter and sugar in a food processor or with a hand-held whisk until light and fluffy (about 2 minutes).
Whisk in the eggs one by one, then stir in the lemon zest and juice.
Fold in the flour, almonds and poppy seeds, then pour the batter into the cake tin.
Bake for 30 to 35 minutes, or until a skewer poked into the middle of the cake comes out almost clean.
For the topping
EITHER
(Option 1) Heat the juice from the 1½ lemons with the caster sugar until the sugar has dissolved. When the cake has just come out of the oven, poke the cake all over with a skewer or fine knife, then pour the syrup all over the cake. Let cool, and serve.
OR
(Option 2) Add the lemon juice to the icing sugar to make lemon icing. Pour/Spread the icing over the cake (don’t worry if it drips down the sides of the cake – it’s supposed to do that!). Let the icing set, then serve.