In a saucepan, warm the heavy cream and butter on low heat just so the butter can melt. Add salt.
Slowly add the warm cream mixture to the matcha and whisk or stir until there aren't any clumps. It'll also help if you sift the matcha first. Set aside.
Rough chop the white chocolate and put into a large stainless steel or glass bowl.
Put about four cups of water in a pot to boil. After the water comes to a boil, turn off the heat and place the bowl of chocolate on the pot for the chocolate to melt slowly. Stir occasionally with a spatula.
Once the chocolate has melted completely, take the bowl off the pot and pour in the matcha cream into the chocolate. Mix well.
If the chocolate starts to separate or look grainy, add in a tablespoon of hot water and the chocolate mixture/ganache will come back together. Add another tablespoon of water if needed.
Pour the ganache into a piping bag or a plastic storage bag. Pipe the ganache into silicone molds. To get a smooth and even surface, scrape off the top of the mold with a dough scraper.
Put the molds into the fridge for about 4-5 hours to solidify. Once solidified, carefully pop the cubes of ganache out of the molds.
Sift some matcha on a plate and coat each cube of ganache. Crush some freeze-dried raspberries on the same plate and sprinkle on top.