Preheat the oven to 180°C (fan)/200°C/gas mark 6.
Line a baking tray with non stick baking paper and set aside.
First mix together your cinnamon sugar. Place 50g brown or coconut sugar into a bowl and add 1 teaspoon ground cinnamon. Mix to combine. Set aside.
Weigh out 350g self raising flour, ½ teaspoon bicarbonate of soda, 1 teaspoon ground cinnamon and a pinch of salt (optional) and place in a mixing bowl. Use a whisk to mix together. If you're adding sugar to your dough add that now too (2-4 tbsp).
Place 75ml milk into a jug and add ½ tablespoon lemon juice.
Pour over the flour mixture and stir to combine.
Add 300g sweet potato purée and mix again into a rough dough*.
Knead in the bowl for a minute or two until you have a smooth ball of dough.
Lightly flour a work surface and pat or roll the dough out into a rectangle that is roughly the same size as a sheet of A4 paper**.
Sprinkle over the cinnamon sugar leaving a 3cm border at the end closest to you.
Starting from the edge furthest away from you roll one of the long edges of your dough up into a spiral shape, pressing with your fingers as you go. If your dough is sticking to the work surface you may find a dough scraper helps.
Once you have a long spiral shape use a sharp knife to cut into 10 rounds and place cut side down on your prepared baking tray.
Bake in the oven for 25-30 minutes until turning golden brown.