Melt the white chocolate in a heatproof bowl using a double boiler or in the microwave in 20-second intervals, stirring in between until completely smooth.
Sift in the matcha powder and whisk until fully combined and smooth.
Line a 15x10-inch baking tray with parchment paper. Pour the matcha chocolate into the tray and spread it into a thin, even layer — it won’t go all the way to the edges and that’s okay.
Place the tea biscuits on top, spacing them out with about ½ inch between each biscuit and around the edges. Gently press each one into the chocolate so the bottoms are embedded but still fully visible on top.
Chill the tray in the fridge for just about 10 minutes, or until the chocolate is just set to the touch. You don’t want it to get too cold or hard, or it’ll crack when you slice it.
Once set, lift the parchment paper out of the tray and place it on a cutting board. Use a sharp knife to slice cleanly between the biscuits. If the chocolate feels too hard, let it sit at room temperature for a few minutes before cutting.