On a piece of tin foil/on a plate, dollop the 6 tsp of chocolate hazelnut spread. Place in the freezer for 30 minutes (longer is fine!).
Preheat the oven to 200C/180C Fan/Gas 6. Spray a 6 hole muffin tray with oil/vegan butter spray.
In a large bowl, combine the milk and vinegar and let sit a few minutes. Add the butter.
Add in the dry ingredients: flour, baking powder, baking soda, cinnamon and sugar. Stir together until just combined. Spoon about 1 tbsp batter into each muffin hole. Add a frozen chocolate spread ball to each, before topping with the remaining batter.
Bake 12-15 minutes until a skewer comes out clean and the tops have gone a little golden.
Whilst these cool on a wire rack, melt the butter. Separately, combine the sugar and cinnamon. Once cool enough to handle, brush the melted butter over the muffins and sprinkle over the cinnamon sugar mix! Best eaten slightly warm, but still delicious cool!