Carrot cake muffins with walnut crumble

Name: Carrot cake muffins with walnut crumble
Prep time: 15 min
Cook time: 40 min
Total time: 40 min
Yield: 8 portions
Ingredients: 120 g rolled oats; 40 g halved walnuts; 2 tbsp mixed seeds; ¼ tsp ground cardamom; ½ tsp ground cinnamon; 120 g unsalted butter; 70 g light brown sugar; 180 g carrot; 50 g plain flour; 2 eggs; ½ tsp bicarbonate of soda; ½ tsp baking powder; 1 pinch salt