Prepare and cool the graham cracker crust, as directed.

Prepare the chocolate cream filling. Place chopped chocolate, butter, and vanilla in a medium bowl and set a fine mesh sieve over top.

Whisk sugar, cornstarch, and salt together in a medium saucepan. Add milk and egg yolks, whisking until completely smooth. Bring to a simmer over medium-low heat, whisking constantly, about 4-5 min. After it bubbles continue cooking for 1½ minutes, whisking, until pudding is thickened to the texture of thin yogurt.

Run the custard through the sieve set over the chocolate. Let sit for 2 minutes, then stir until completely melted and smooth.

Spread chocolate pudding into the cooled crust and chill until firm and ready to serve, at least 2 hours or up to 2 days. (cover with plastic wrap if storing for more than a few hours).

When ready to serve, prepare the meringue. Bring a small skillet filled halfway with water to barely a simmer over low heat. In the bowl of the stand mixer (or a heatproof bowl if using a hand mixer), combine the egg white, cream of tartar, and sugar. Hold the bowl just touching the warm water and stir constantly with a silicone spatula until the sugar is dissolved and the mixture is fully combined and no longer gritty, about 2 minutes. Remove from heat.

With the stand mixer with the whisk attachment (or a hand mixer). whip the mixture on high for 4 minutes until soft white peaks form. In two parts, sift in the matcha, whipping and scraping down the sides between each addition. Beat for another minute until it is bright green and glossy with stiff peaks.

Spread and swirl the meringue over the chilled chocolate custard. Use a kitchen torch to toast the outside of each meringue for a few seconds and serve immediately. Because of the meringue on top, this matcha pie is best eaten the same day it's made. Over time, the meringue tends to lose its texture and separate. If not serving immediately, store in the fridge until ready to slice and serve.