Heat the oven to 180c/160cfan/gas 4 Grease and line a 2lb loaf tin with baking parchment. Butter the parchment on the inside of the parchment. Sprinkle 2 tsp of sesame seeds on the base and sides of the tin.
Whisk the caster sugar and egg together pale, thick and the sugar has dissolved. Add the yoghurt, milk, sesame oil, cinnamon and vanilla paste. Whisk until smooth. Add the flour, baking powder, bicarbonate of soda and the remaining sesame seeds, fold in until well combined.
Pour into the mixture into the prepared tin and smooth the top to level. Cut the apple in quarters and remove the core. Slice around 2mm thick and arrange on the surface gently pushing into the mixture, sprinkle over the remaining sesame seeds and 1 tsp caster sugar.
Bake for 40-50 minutes until risen, golden brown and a skewer comes out clean when inserted.
Leave to cool completely on a wire rack before slicing.
