Preheat the oven to 180 C. Grease an 8-inch springform tin or line it with non-stick baking paper. Grind the almonds using a blender or food processor until finely ground, making sure you don't run it too long or you'll wind up with almond butter!
In a mixing bowl, beat the butter, sugar and lemon zest until light and fluffy, using a hand mixer on low speed.
Add the eggs and beat briefly to combine. Add the ground almonds, semolina and baking powder mixture and beat slowly until combined. Stir in the lemon juice. Do not over-mix.
Transfer the batter into the prepared tin and smoothen the top. Bake for 25 to 30 minutes, or until browned on top and a toothpick comes out clean or with a few moist crumbs.
Five minutes before the cakes are done, make the syrup. Combine the sugar and lemon juice in a small saucepan on medium heat and stir together. Bring to a boil, and simmer for 3 to 4 minutes, stirring to make sure the sugar dissolves. It will thicken very slightly.
Immediately spoon the syrup over the top of the hot cake and leave to cool completely, preferably overnight. The cake can be stored at room temperature for a couple of days but I found it tasted best cold from the fridge and the pieces are firmer too. In the fridge it'll last for 5 to 6 days. Happy baking!