Whisk the dry ingredients: In a medium bowl, whisk together the plain flour, baking powder, bicarbonate of soda, and salt until they are evenly combined. You'll see the mixture look light and uniform, with no streaks of white powder.

Cream the butter and sugar: In a large bowl, beat the softened butter and caster sugar together with a hand mixer or stand mixer on medium speed until the mixture turns pale yellow and looks fluffy, about 2 minutes. It should smell sweet and buttery, and the texture will feel light and airy.

Add the wet ingredients: Beat in the egg, fresh lemon juice, lemon zest, and vanilla extract. The batter will look slightly curdled at first, which is normal, but keep mixing until it becomes smooth and glossy. The aroma of lemon will fill your kitchen.

Combine wet and dry: Gradually add the flour mixture to the wet mixture, mixing on low speed just until no streaks of flour remain. The dough will be very soft and slightly sticky, almost like a thick paste. Do not overmix, or the cookies will be tough.

Chill the dough: Cover the bowl with cling film and refrigerate for at least 30 minutes. The dough will firm up significantly, becoming less sticky and easier to handle. This step is crucial for preventing the cookies from spreading too much.

Preheat and prepare: Preheat your oven to 180°C (160°C fan). Line a baking tray with parchment paper. Place the icing sugar in a shallow bowl.

Roll and coat: Using a tablespoon or a small cookie scoop, portion the dough into balls about 2.5cm in diameter. Roll each ball between your palms until smooth, then drop it into the icing sugar. Roll it around to coat generously, pressing gently so the sugar sticks. The ball should look like a little snowball.

Bake: Place the dough balls 5cm apart on the prepared baking tray. Bake for 10-12 minutes. The cookies are ready when the edges are set and lightly golden, but the centres still look soft and slightly puffed. They will have crinkled on top, with cracks showing the pale yellow dough through the white sugar.

Cool: Let the cookies cool on the baking tray for 5 minutes. They will continue to set as they cool. Then transfer them to a wire cooling rack to cool completely. The bottoms should be lightly golden and the tops perfectly crinkled.