Grease or line a 12 cup muffin pan with cup cake liners.
Use a handheld blender or stand mixer to cream the butter, oil, and sugar. Add in the buttermilk and continue beating until combined.
Stir in the baking powder, baking soda, ground cinnamon powder, salt and vanilla extract.
Add in the flour alternating with the milk. Mix until just combined. Do not overmix
Divide two-thirds of the mixture between the muffin cups.
Carefully add one teaspoon of jam into the centre of each, then cover with the remaining mixture. If you do not want to use jam, then please feel free to leave it out. Simply fill the muffin cups up to ¾ full with the batter.
Bake in a preheated oven of 320°F (160°C ) for 15 to 20 minutes until risen, golden and springy to touch. Leave the muffins to cool for 5 mins before lifting out of the tin and rolling in the melted butter and cinnamon sugar. See note 5