Preheat the oven to 160°C/325°F/gas mark 3. Butter a 450g/1lb loaf tin, then line with baking parchment.
Put the melted butter in a bowl and add the eggs and sugar. Mix together to a smooth paste, then beat in the almond butter and mashed bananas.
Sift the flour, baking powder and salt into a separate bowl, then gradually fold the flour mixture into the banana mixture. Stir in the chopped chocolate and spoon the mixture into the prepared loaf tin.
Bake in the oven for 55 minutes, or until a wooden skewer inserted into the centre comes out clean. Leave to cool in the tin on a wire rack for about 10 minutes, then turn out of the tin onto the wire rack and leave to cool some more.