Pulse freeze-dried raspberries in a blender or food processor until reduced to a powder.
Place caster sugar, cocoa powder, oil, baking powder, vanilla, salt and 4 tablespoons of the powdered raspberries in a large bowl. Beat together with a mixer until well blended. Mix in eggs 1 at a time, waiting until each addition is incorporated before adding the next. Add flour; mix on low speed until incorporated. Cover with cling film. Chill 4 to 8 hours or overnight.
Preheat oven to 180 C / Gas 4. Line a baking tray with a silicone baking mat or baking parchment.
Place icing sugar in a small bowl. Place remaining powdered raspberries in another small bowl.
Roll walnut-size pieces of cookie dough into a ball, then roll each ball partly in powdered raspberries and partly in icing sugar. Arrange on prepared tray and bake until barely set and crackled on top, 10 to 12 minutes. Cool on sheet 10 minutes. Transfer to a wire rack to cool completely.
Cookies keep up to 3 days in an airtight container at room temperature, or up to 3 months frozen.
These are available in the baking section in many large supermarkets and in specialist cake shops.