Prep the pan: Line the bottom of a 9-inch springform pan with parchment. Wrap the outside of the pan with two layers of heavy-duty foil to keep water out.
Make the crust: Mix graham crumbs, sugar, salt, and melted butter until it feels like damp sand.
Press firmly into the bottom (and a bit up the sides) of the pan. Bake at 350°F (175°C) for 8–10 minutes. Cool slightly while you make the filling.
Reduce oven to 325°F (160°C).
Prep the matcha: Sift matcha into a small bowl to remove lumps. This step matters—matcha can clump and cause specks in your batter if you skip it.
Beat the cream cheese: In a large bowl, beat cream cheese on medium-low until smooth, about 1–2 minutes. Scrape the bowl.
Add sugar and beat another minute until creamy and lump-free.
Add matcha and dry mix: Beat in the sifted matcha, cornstarch, and salt on low until combined. The color should turn evenly green.
Blend in the wet ingredients: Add sour cream and vanilla; mix on low until silky. Add eggs one at a time, mixing on low and scraping the bowl between each.
Stop as soon as the batter is smooth—overmixing adds air and leads to cracks.
Assemble the water bath: Place the foil-wrapped pan in a large roasting pan. Pour the filling into the crust. Tap the pan gently on the counter to release air bubbles.
Pour hot water into the roasting pan to come halfway up the sides of the springform.
Bake: Bake at 325°F (160°C) for 55–70 minutes. The edges should be set, and the center should still slightly wobble like gelatin. If it looks liquid in the center, give it 5–10 more minutes.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake rest inside for 45 minutes.
Then remove from the water bath and cool on a rack to room temperature.
Chill: Cover and chill at least 6 hours, preferably overnight. This sets the texture and deepens the flavor.
Serve: Run a thin knife around the edge before unlatching the springform. Slice with a hot, clean knife, wiping between cuts.
Dust lightly with matcha, add whipped cream, and top with berries if you like.