Line a baking sheet with parchment paper. Using a pencil, draw a 9" by 10" rectangle lengthwise in the middle of the parchment. Flip the paper over so you can see the rectangle, but the pencil won't rub off.

Place 3/4's of the bittersweet chocolate in a medium glass bowl. Microwave on high for 30 seconds, then stir the chocolate. Microwave on high again for 30 seconds, then stir the chocolate. Continue microwaving at 30 second intervals and stirring until the chocolate is just melted. Stir in the remaining bittersweet chocolate until smooth. Microwave for an additional 15 seconds on high if the chocolate isn't fully melting.

Pour the chocolate on to the prepared baking sheet, and gently smooth it out to fit the rectangle (doesn't have to be perfect). Transfer to the refrigerator and let chill for 15 minutes.

Melt white chocolate using the same method above (30 seconds of cooking, then stir). Pour 1/4 cup melted white chocolate into a measuring cup with a pour spout and set aside. Stir matcha into remaining chocolate until smooth. Pour green matcha chocolate over the dark chocolate layer, and gently smooth to evenly cover. Zigzag reserved white chocolate over the surface of the bark, then, using a skewer to toothpick, swirl the white chocolate into the green matcha chocolate. Sprinkle the surface of the chocolate evenly with toasted pistachios and sea salt, gently pressing down on the pistachios.

Let the bark sit at room temperature for at least 2 hours, so the chocolate can firm up. Using a sharp knife, carefully cut the bark into pieces. Store in an airtight container at room temperature for up to 2 weeks.