Line 9 sections of a 12-section bun tray with paper cake cases. Scrub the sweet potato and cut into chunks. Cook in a saucepan of boiling water for 10 minutes or until tender. Drain well and return to the pan. Mash until smooth and leave to cool.
Crush the cardamom pods in a mortar with a pestle to release the seeds. Discard the shells and crush the seeds as finely as possible.
Melt the butter in a small saucepan with the honey. Turn into a bowl and leave to cool slightly. Beat in the sweet potato and cardamom, then the eggs, flour and baking powder.
Divide the cake mixture between the paper cases and scatter with the flaked almonds.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes or until risen and just firm. Transfer to a wire rack to cool.
Beat the sugar with the lemon juice in a bowl to make a smooth, thin glacé icing. Drizzle thin lines of icing back and forth across the cakes.