Preheat your oven to 180°C (160°C fan). Line a small baking tray with baking parchment or lightly grease a small oven-safe ramekin.

In a small bowl, prepare the topping by mixing the 1 tbsp of granulated sugar and 1/4 tsp of ground cinnamon together with a fork. Set aside.

In a separate medium bowl, use a fork or a small spatula to cream together the softened unsalted butter and 2 tbsp of granulated sugar until the mixture is light and fluffy. This should take about a minute.

Add the beaten egg and vanilla extract to the butter mixture and mix until just combined. Don't worry if it looks a little split at this stage.

In the same bowl, add the plain flour, cream of tartar, bicarbonate of soda, and the pinch of salt. Gently fold the dry ingredients into the wet ingredients until a soft dough forms. I find it's best to stop mixing as soon as you no longer see any dry flour streaks to avoid a tough cookie.

Shape the dough into a ball with your hands. Roll the ball generously in the cinnamon-sugar mixture until it is completely coated.

Place the coated dough ball onto your prepared baking tray or into the ramekin. Gently flatten the top ever so slightly with your palm.

Bake for 10-12 minutes, or until the edges are set and golden brown, and the centre is still soft. The cookie will spread and form delightful cracks on top.

Allow the cookie to cool on the baking tray for at least 5 minutes before transferring it to a wire rack. This is crucial as it will be very soft straight out of the oven and needs time to set up. Enjoy it warm!