Cream the butter and sugars. In a large bowl, beat the softened butter with both sugars until the mixture turns pale and fluffy — about 3 to 4 minutes with an electric mixer. You'll see the colour lighten noticeably, and the texture will feel airy and soft against the beaters. The sugar granules should be mostly dissolved into the fat.

Add the eggs and vanilla. Crack in the eggs one at a time, beating well after each addition until the mixture is smooth and glossy. Stir in the vanilla extract. The batter should look thick and almost satiny, with no streaks of egg white remaining.

Whisk the dry ingredients. In a separate bowl, whisk together the flour, bicarbonate of soda, cinnamon, nutmeg, and salt until evenly combined. The spices should release a fragrant, warming aroma as you stir them through the flour.

Combine wet and dry. Gradually add the flour mixture to the butter mixture, mixing on low speed just until no dry flour remains. Scrape down the sides of the bowl once or twice. The dough will be stiff and cohesive, but don't overmix — you want a tender crumb, not a tough one.

Fold in the oats and raisins. Tip in the rolled oats and raisins, and fold them through with a wooden spoon or spatula. The oats should be evenly distributed, and every raisin should be tucked into the dough. The mixture will look bumpy and hearty, with the oats giving it a rustic, textured appearance.

Chill the dough. Cover the bowl with cling film and refrigerate for at least 30 minutes, or up to 24 hours. This step is crucial — the cold dough spreads more slowly in the oven, giving the oats time to soften and the flavours to meld. The dough will feel firm and slightly tacky to the touch when ready.

Preheat and prepare. Heat your oven to 180°C (160°C fan) and line two baking trays with parchment paper. Scoop rounded tablespoons of dough (about 45g each) and roll them into balls. Place them 5cm apart on the trays — they will spread a little, but not excessively.

Bake until golden. Bake for 12 to 14 minutes, rotating the trays halfway through. The cookies should look puffed and lightly golden around the edges, while the centres remain pale and slightly soft. You'll smell a deep, toasty fragrance of oats and caramelised sugar filling your kitchen.

Cool on the tray. Let the cookies rest on the baking tray for 5 minutes — they will continue to set from the residual heat. The edges will firm up beautifully while the centres stay tender. Then transfer them to a wire cooling rack to cool completely, or enjoy one warm for the ultimate treat.