Scoop 12 blobs of white chocolate spread (about 1 tbsp each). Freeze on a parchment-lined tray for at least 30 minutes (preferably overnight).
In a bowl, whisk together flour, self-raising flour, black cocoa, salt, and baking powder.
In another bowl, lightly whisk 2 whole eggs + 1 yolk. Set aside.
In a stand mixer, combine cold chopped butter, brown sugar, and caster sugar. Mix on low until chunky (1-2 min). Do not overmix.
Add white chocolate chips, dark chocolate chips, and 50g crushed Oreo crumbs. Mix briefly.
Add dry ingredients. Mix until texture is sandy (like wet sand).
Add whisked eggs. Mix just until dough comes together. Do not overmix.
Portion dough into 125g balls. Do not roll smooth – keep craggy.
Press a frozen white chocolate blob into the center of each dough ball. Seal edges gently.
Roll each filled dough ball in extra Oreo crumbs (50g).
Freeze dough balls on a tray for at least 4 hours (ideally overnight).
Preheat oven to 190°C (375°F) fan. Place frozen dough on baking sheet, spaced apart. Bake for 16 minutes. Do not open oven.
Cool on baking sheet for 10-15 minutes before transferring to a wire rack.