1 In a non-stick pan, toast sesame seeds until golden brown. Place on a small plate and let cool.
2 Rinse and dry plums. Cut in half and remove pits. Cut 12 slices and reserve. Finely dice the remaining flesh.
3 Mix flours, sugar, cream of tartar and 1 pinch of salt in a mixing bowl. Add buttermilk, egg, oil and about 2/3 of the sesame seeds. Using a hand mixer, mix to form a smooth batter.
4 Fold in the diced plums. Line the muffin tin with 12 baking cups and fill using a spoon.
5 Top the muffins with the reserved plum slices. Sprinkle with remaining sesame seeds and bake in a preheated oven on the middle rack at 180°C (convection oven 160°C, gas mark 2-3) (approximately 350°F/convection 325°F) for about 25 minutes.
6 Let muffins cool for about 5 minutes in the muffin tin, then remove muffins from tin and let cool completely on a wire rack.