Pre-heat the oven to 200°C/180°C fan/gas mark 6. Line a 12-hole muffin tray with paper cases (or grease thoroughly with some extra butter if you don’t have paper cases).
Sift together the flour, baking powder and bicarbonate of soda, then stir in the cardamom and salt. Stir in the white chocolate.
In a separate bowl, mash together the bananas, sugar, egg, melted butter, vanilla and tahini.
Mix the wet ingredients into the dry, being careful not to over-mix – this is the key to a light muffin. Divide between the 12 cases and bake the muffins for 20–25 minutes, until they spring back when pressed lightly with a finger.
Transfer the muffins in their cases to a wire rack to cool.
Make the glaze. In a small bowl, whisk together the tahini, icing sugar, lemon juice and two tablespoons of water. When the muffins are cool, spoon the glaze over the top. Sprinkle with the sesame seeds and leave for an hour or so for the glaze to set before eating (if you can wait!).