Line a 12-hole nonstick muffin tin with paper muffin cases or lightly grease. Sift the flour, baking powder and salt into a large bowl, then stir in the sugar, bran and chocolate chunks.
Beat together the eggs, melted butter, buttermilk and banana in a jug. Pour into the dry ingredients, add the raspberries and stir until just combined.
Spoon the mixture into the prepared muffin tin and top each muffin with a banana chip. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 18–22 minutes until risen and firm to the touch. Serve warm.