You can substitute plain flour with whole wheat flour, though muffins may be denser. Replace caster sugar with granulated sugar if needed. For a dairy-free version, use almond milk and vegan butter. Muffins are best enjoyed fresh but can be stored in an airtight container at room temperature for 2 days, or frozen for up to 1 month. If muffins stick to the tin, ensure it is well-oiled and allow them to cool briefly before removing. If muffins are dry, check oven temperature or reduce bake time. Re-coat muffins with cinnamon sugar before serving for maximum flavor.