Preheat and prepare. Heat your oven to 180°C (160°C fan) and line two large baking trays with baking parchment. While the oven heats, you can get everything else done.

Cream the butter and sugars. In a large bowl, beat the softened butter, caster sugar, and brown sugar together until light and fluffy. You’ll know it’s ready when the mixture looks pale, almost like a thick paste, and smells sweetly of caramel. This takes about 3 minutes with an electric mixer, or 5 minutes by hand.

Add the wet ingredients. Beat in the egg and vanilla extract until fully combined. The mixture will look slightly glossy and a bit looser than before. Scrape down the sides of the bowl with a spatula.

Combine the dry ingredients. In a separate small bowl, whisk together the plain flour, bicarbonate of soda, and salt. This ensures the raising agent is evenly distributed so every cookie rises uniformly.

Mix the dough. Gradually add the dry ingredients to the wet mixture, stirring gently with a wooden spoon or spatula. Stop mixing as soon as you no longer see streaks of flour. The dough will be thick and slightly stiff, but not dry. Overmixing develops gluten, which makes tough cookies.

Fold in the sprinkles. Gently fold the sprinkles into the dough with a few swift turns of your spatula. Be careful not to overmix here, or the colour from the sprinkles will bleed into the dough, turning it a murky grey. The dough should look like a starry night sky, with bright specks of colour.

Scoop and arrange. Using a tablespoon or a cookie scoop (about 1.5 tablespoons of dough), roll the dough into balls and place them 5cm apart on the prepared trays. Do not flatten them; they will spread as they bake.

Bake until golden. Bake for 10-12 minutes. The edges should be a light golden brown and look set, while the centres will still appear slightly puffed and soft. They will look slightly underdone in the middle – that is the secret to a chewy cookie. The smell of vanilla and toasting butter will fill your kitchen.

Cool on the tray. Leave the cookies to cool on the baking tray for 5 minutes. They will continue to cook from the residual heat, setting the centre perfectly. After 5 minutes, transfer them to a wire rack to cool completely. The tops will be crackled and the edges crisp.