Preheat and prepare: Set your oven to 180°C (160°C fan). Line two baking trays with baking parchment. You'll hear the fan kick in when it's up to temperature.

Cream butter and sugar: In a large bowl, beat the softened butter and 200g of caster sugar together until the mixture looks pale, fluffy, and slightly grainy — like wet sand. The colour should shift from bright yellow to a soft cream.

Add wet ingredients: Crack in the egg and add the vanilla extract. Stir vigorously until the mixture is smooth, glossy, and has a thick, ribbon-like texture when you lift the spoon.

Combine dry ingredients: In a separate small bowl, whisk the flour, cream of tartar, bicarbonate of soda, and salt together. Tip these into the wet mixture and fold gently with a spatula until just combined. The dough will be soft, slightly sticky, and smell faintly of warm vanilla.

Make the coating: In a shallow bowl, mix the 3 tablespoons of caster sugar with the ground cinnamon. The aroma should be fragrant and spicy.

Shape and coat: Using your hands, roll tablespoon-sized balls of dough (about 30g each). Drop each ball into the cinnamon sugar, rolling it around until completely coated. Place them on the baking trays about 5cm apart — they will spread slightly.

Bake: Slide the trays into the oven and bake for 9–11 minutes. At 9 minutes, the edges should be set and lightly golden brown, but the centres will still look puffy, soft, and slightly underdone. The kitchen will smell like a bakery.

Cool: Leave the cookies on the tray for 5 minutes — they will continue to set as they cool. Then transfer them to a wire rack. The tops should crackle beautifully, revealing a soft, chewy interior.