Preheat your oven to 180°C/350℉ (160°C/325℉ for fan and convection ovens). Then line a large tray or two with baking paper.
Add the softened butter to a bowl with the caster sugar and brown sugar. Mix well to make a thick paste.
Add the egg and vanilla extract then mix until smooth.
Add all of the self-raising flour, the ginger and the cinnamon and mix it in. When it starts to come together, use your hands to press it into a ball of dough.
Add the white chocolate chunks, saving a few for the top, and gently knead them into the dough with your hands.
Divide the dough into 12 equal-sized pieces and roll into balls. Lightly press them down until around 1 inch thick.
Place the cookies on the tray, leaving a couple of inches between them to allow for spreading. Around 4-5 per tray works best.
Top with extra chunks of white chocolate.
Bake for 11-12 minutes until they're just turning golden brown at the edges. They will look underbaked in the middle but resist the urge to keep baking- they will firm up as they cool.
Let the cookies cool completely before removing them from the tray.