Preheat the oven to 200C/180C Fan/Gas 6. Line a 6 hole muffin tin.
In a large bowl, combine the dry ingredients (flour, baking powder, sugar, cinnamon, salt).
Make a well, and pour in the liquid ingredients (milk, butter, oil and egg). Stir gently with a wooden spoon until just combined.
Scoop the batter evenly into each muffin hole, filling up to 2/3rds full.
Combine the tbsp sugar and tsp cinnamon in a small bowl and sprinkle over the muffins before baking. Bake for 18-20 minutes - until golden brown on top.
Let the muffins cool on a wire rack a little before making holes in the muffins for the ganache. Do this by using the end of a wooden spoon, or a piping nozzle - to create small holes in the centre of each muffin.
Make the ganache by first chopping the chocolate as small as possible. Add the chocolate to a heat proof (e.g. Pyrex) jug.
Then heat the cream in a pan on a very low heat (or the microwave, checking on it at 10 second intervals) until it feels hot (it should just start to bubble at the edges). Pour the cream over the chocolate and let sit for 1 minute before stirring together to form a chocolate ganache.
Pour this mixture into the holes of each muffin. You may find the level drops as some cream/ganache mixture gets into the cracks of the muffins, so top up after 2 minutes if you want!
Let set in the fridge for about 30 minutes before serving!