Mix all the ingredients in a bowl until smooth.
Pour the batter into a 15cm (6-inch) round tin lined with baking paper. Tap to level it out and cover with foil.
Bake at 180°C (350°F) for 50 minutes, removing the foil after 20 minutes.
Let it cool in the tin for 20 minutes, then transfer to a plate (keep the baking paper on for now).
Refrigerate for 2 hours to set.
