Preheat oven to 200°C/400°F/Gas Mark 5. Line a loaf tin with baking paper. Beat caster sugar, eggs and lemon verbena together until pale-coloured and fluffy. Lightly whisk in oil and wine. Sieve flour, baking powder and polenta together and gently stir in. Pour batter into prepared loaf tin and bake in the centre of the oven for 15 minutes, then cover the tin loosely with foil and turn the oven down to 170°C/340°F/Gas Mark 3–4. Bake a further 25 minutes. Test by inserting a skewer into the deepest part. It should come out a little moist but clean. Remove the foil and cool on a cake rack.
To serve, slice cake and dollop on chocolate cardamom cream. This is also excellent served with poached pears or stone fruit.