Prepare Your Dry Ingredients: In a medium bowl, whisk together the plain flour, bicarbonate of soda, baking powder, and salt. This step ensures the raising agents are evenly distributed. Set it aside.

Cream Butter and Sugars: In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the softened butter, granulated sugar, and light brown sugar on medium-high speed for about 3-4 minutes. The mixture should become light, pale, and fluffy. This process incorporates air, which is key to the cookie's texture.

Add Egg and Vanilla: Scrape down the sides of the bowl. Add the room temperature egg and vanilla extract and beat on medium speed until just combined, about 30 seconds. Don't overmix at this stage.

Combine Wet and Dry: With the mixer on its lowest speed, gradually add the dry flour mixture to the wet ingredients. Mix until the flour is almost fully incorporated, but you can still see a few streaks. This is important to avoid developing too much gluten.

Fold in the Goodies: Remove the bowl from the mixer. Gently fold in the chopped white chocolate and the frozen raspberries with a spatula until they are just evenly distributed. I find it’s best to work quickly here so the raspberries don't thaw and stain the dough too much.

Chill the Dough: Cover the bowl with cling film and place it in the refrigerator to chill for at least 30 minutes (or up to 48 hours). Chilling the dough is a crucial step; it solidifies the butter, which prevents the cookies from spreading into thin, crispy discs in the oven. For a deeper dive into the science behind this, Serious Eats has a great explanation of how resting dough improves flavour and texture.

Preheat and Prepare: While the dough is chilling, preheat your oven to 180°C (160°C fan) and line two large baking trays with parchment paper.

Portion and Bake: Scoop out portions of dough, about 2 tablespoons each, and roll them into balls. Place them on the prepared baking trays, leaving at least 5cm (2 inches) of space between each one to allow for spreading. I like to press a few extra chunks of white chocolate on top of each ball for a prettier finish.

Bake to Perfection: Bake for 12-15 minutes, or until the edges are lightly golden brown and the centres look slightly underdone. The cookies will continue to cook on the hot tray after you remove them.

Cool Down: Let the cookies cool on the baking trays for 5-10 minutes before carefully transferring them to a wire rack to cool completely. This helps them set up properly.