Line a 9x13-inch baking sheet with parchment paper, letting the paper hang over the edges for easy removal later.

Melt 10 oz of the white chocolate in a microwave-safe bowl in 30-second intervals, stirring between each, until completely smooth and fluid. This takes about 90 seconds total.

Remove 1/4 cup of the melted white chocolate and set aside in a small bowl. Add the sifted matcha powder to the remaining chocolate and whisk vigorously until completely smooth with no streaks or clumps.

Pour the matcha chocolate onto the prepared baking sheet and spread into an even layer about 1/4-inch thick using an offset spatula.

Drizzle the reserved plain white chocolate over the matcha layer in random lines. Use a toothpick or skewer to swirl the two colors together, creating a marbled effect. Tap the pan firmly on the counter 3-4 times to smooth the surface.

If using toppings, sprinkle them over the bark immediately while the chocolate is still wet. Refrigerate for 30-45 minutes until completely firm.

Lift the bark out using the parchment paper overhang and break into irregular pieces with your hands. Store in an airtight container.