Pre-heat the oven to 180C(360F) fan-forced.
Line a 6-hole muffin tin with muffin papers.
Place the butter, honey and vanilla in a heat-proof jug and microwave it in short bursts until the butter has melted. Combine the butter jug contents with the mashed banana in a big bowl.
Add the flour, baking powder, baking soda, cinnamon, mixed spice, salt and walnuts and stir until the mixture is just combined. You don't want to over mix muffins - they're meant to be lumpy.
Spoon the mixture into the paper cases and leave to sit for a few minutes.
Bake for 25 minutes.
Leave to cool slightly in the tin then gobble them up (or transfer to a wire rack to cool completely).