Banana and Oat Muffins

Name: Banana and Oat Muffins
Prep time: 10 min
Cook time: 35 min
Total time: 35 min
Yield: 12 pieces
Ingredients: 70 g unsalted butter; 250 g wholemeal flour; 100 g golden caster sugar; 1 level Tbsp baking powder; 1 pinch fine sea salt; 2 large eggs; 125 g milk; 280 g ripe bananas; 60 g walnut halves; ½ tsp ground cinnamon; ½ tsp ground nutmeg; 20 g jumbo oats