Melt the dark chocolate chips with half the coconut oil in 30-second microwave bursts, stirring between each, until smooth and glossy. Repeat separately with the white chocolate chips and remaining coconut oil.

Pour the dark chocolate onto the parchment-lined sheet and spread it to about 0.6 cm (0.25 in) thick using a spatula.

Drop spoonfuls of the white chocolate over the dark chocolate at irregular intervals.

Drag a skewer or toothpick through both layers in long sweeping motions to create a marble or swirl pattern.

While both chocolates are still fluid, scatter the Halloween candy pieces, pretzel pieces, sprinkles and black sanding sugar across the entire surface, pressing gently so they adhere.

Leave the bark flat at room temperature for 1 hour, or refrigerate for 20 minutes, until completely set.

Break into irregular shards by pressing firmly at the centre and snapping outward. Pile on a board for serving.