Line a 10x15 inch baking sheet with parchment paper or a silicone mat.

Melt the white candy melts in a microwave-safe bowl in 30-second intervals, stirring between each, until completely smooth.

Melt the green candy melts in a separate small microwave-safe bowl using the same 30-second interval method.

Pour the melted white chocolate onto the prepared baking sheet and spread evenly to approximately 1/4-inch thickness using an offset spatula.

Drop small dollops of the melted green chocolate across the surface of the white chocolate.

Drag a toothpick or a clean knife through the dollops to create a marbled swirl pattern.

Immediately press the marshmallows and crushed pretzels into the wet chocolate.

Distribute the gold sanding sugar and shamrock sprinkles evenly over the top.

Place the baking sheet in the refrigerator for 30 minutes or until the bark is completely firm.

Remove from the refrigerator and break the bark into irregular pieces by hand or with a sharp knife.

Store in an airtight container at room temperature for up to two weeks.