Preheat the oven to 180℃/160℃ fan/350℉/gas mark 4. Grease a 23 cm/9 in round or 20 cm/8 in square baking dish or cake tin.
Mix together the ground almonds, plain flour, cornflour, sugar and baking powder in a large bowl.
Add the yogurt, melted butter, elderflower cordial and lemon zest and stir with a balloon whisk until no dry lumps remain.
Transfer the batter to the greased baking dish and spread level, bake for 30-40 minutes until a skewer inserted into the centre comes out clean.
While the pudding is baking, mix together the cordial and lemon juice for the drizzle in a small jug.
When the pudding is baked, allow it to cool for 5 minutes then poke holes in the top all over with a cocktail stick. Pour over the drizzle evenly, making sure to go round the sides as well as in the middle.
Serve warm with ice cream.