Preheat your oven to 180°C (160°C fan) and line a large baking tray with baking parchment. The paper should feel crisp and dry to the touch once the oven reaches temperature.

Cream the butter and sugars together in a large bowl using a wooden spoon until the mixture looks pale, fluffy, and light — you'll notice it becomes noticeably lighter in colour, almost like a sandy paste. This should take about 2 minutes of steady stirring.

Add the egg and vanilla extract, then beat vigorously until the mixture is smooth and glossy. You'll see it become shiny on the surface, and the smell of vanilla will fill your kitchen immediately.

Sift the flour, bicarbonate of soda, cinnamon, and salt directly into the bowl. Fold everything together gently — stop as soon as you can no longer see any streaks of white flour, which usually takes about 10 turns of the spoon.

Stir in the rolled oats and raisins until they're evenly distributed throughout the dough. The mixture will feel quite stiff and slightly sticky when you press it between your fingers, but it should hold together easily without crumbling.

Scoop heaped tablespoons of dough and roll them into balls roughly the size of a walnut. Place them on the prepared tray, leaving about 5cm between each ball — they will spread during baking, so don't be tempted to crowd them.

Bake for 10-12 minutes until the edges are golden brown and the centres still look slightly underdone and puffy. The tops should be set but still soft to a gentle touch; they will continue cooking on the tray after you remove them from the oven.

Leave the cookies on the tray for a full 5 minutes before transferring them to a wire rack. During this time, you'll see the centres settle and become perfectly chewy. The kitchen will smell like a bakery by now, which is the best cue that they're ready.