Toast Vermicelli: Over low-medium heat, melt butter in a medium pan. Add crushed vermicelli; cook, stirring often, for about 10 minutes until fragrant and evenly golden brown. Prevent burning.
Make Pistachio Filling: Cool toasted vermicelli completely. Transfer to bowl. Add pistachio butter and tahini; blend well into a textured filling.
Create Marble Effect (Optional): Gently melt white chocolate. Optional: Drizzle half into moulds. Tint remaining white chocolate with green food colouring; drizzle into moulds. Freeze moulds for at least 5 mins.
Temper Main Chocolate: Combine and temper milk & dark chocolate. Reserve 1-2 tsp. Let rest cool slightly (10-15 mins) until fluid but not hot.
Form Chocolate Shells: Remove chilled moulds. Pour cooled, tempered chocolate into cavities, coating sides well. Refrigerate 20-30 mins until firm.
Add Filling: Spoon/pipe pistachio filling into firm chocolate shells. Mould Tip: For two-part moulds, fill one half, mounding slightly in center for shallower moulds.
Seal Bars (Two-Part Moulds): If reserved chocolate firmed, gently re-warm until fluid. Apply thin coat to edges of filled mould half.
Chill and Set: Carefully join mould halves, pressing gently. Refrigerate for at least 1 hour, or until bar releases easily.
Serve: Enjoy chilled or let soften slightly at room temperature.
Store: Keep leftover bars in an airtight container in the fridge for up to one week.
