Line a muffin tin with silicone cupcake liners. This recipe makes 4 cups, but you can easily triple the amount to fill a 12 cup muffin tin.
Melt white chocolate in a double boiler. If you've never used this method before, you will put white chocolate in a heat proof bowl that can rest on the top of a pot of simmering water (don't let it touch the water). The steam will heat the bowl which will melt the chocolate.
When chocolate is melted, sift in 1/2 teaspoon of strong matcha powder. Stir well to combine, ensuring no streaks of dry powder remain.
Spoon one tablespoon of matcha chocolate into each silicone cupcake. Use the back of the spoon to spread the chocolate to cover the entire bottom of the liner and about 1 cm up the sides.
Return bowl of chocolate to the double boiler to prevent it from hardening. Put cupcake liners in the fridge or freezer to set the chocolate. It should only take a few minutes.
Spoon one tablespoon of pistachio butter into each cupcake liner on top of the chocolate.
Remove chocolate from the double boiler and spoon an additional tablespoon into each cupcake liner, smoothing the chocolate on top of the pistachio butter and to the sides of the cup.
Put tin back into the fridge to set again.
When chocolate is set, remove them from the silicone liners. Any excess chocolate that has spilled or spread from the edges will easily break off.
You can serve matcha chocolate cups immediately or keep in airtight container. Store in the fridge or countertop according to the instructions on the jar of pistachio butter.