Step 1Heat the oven to 300 degrees. Bring a large saucepan of water to a simmer on the stove, then adjust the heat to keep the water at a gentle simmer.
Step 2Meanwhile, place each type of chocolate in a separate bowl.
Step 3In a medium saucepan, combine the cream and milk and bring to a boil. Immediately remove from heat and pour one-third of the hot cream mixture over each of the 3 chocolates and whisk each mixture until the chocolate is melted and the mixture is smooth.
Step 4In each of 3 separate bowls, whisk 2 egg yolks. Whisk 2 tablespoons sugar into the first bowl with the eggs, then whisk in the dark chocolate mixture to form a custard base. Whisk 2 teaspoons sugar into the second bowl with the eggs, then whisk in the milk chocolate mixture to form a custard base. Whisk the white chocolate mixture into the third bowl to form the white chocolate base. Pour each custard base into three small ramekins, custard cups or espresso cups.
Step 5Place the ramekins in a large metal baking pan and place the baking pan in the center of the middle rack in the oven. Pour enough hot water into the baking pan to reach halfway up the sides of the ramekins. Cover the pan with aluminum foil and poke holes in the foil to allow steam to escape.
Step 6Bake the custards just until they are set (the tops will form a "skin" and the custards will jiggle slightly when tapped), about 30 minutes. Gently remove the pan from the oven, remove foil and allow the custards to cool. Wrap the cooled custards with plastic wrap and chill for at least 2 hours.
Step 7Before serving, remove the plastic wrap and place a doily, cutout or stencil over each custard and lightly powder the top with matcha.