Step 1: Preparation and Preheat

1. Preheat Your Oven: Position a rack in the middle of your oven and preheat it to 350°F (175°C).

2. Prepare Your Pan: Grease an 8×8 inch (20×20 cm) square baking pan with butter or non-stick spray. For easy removal and clean-cut slices, create a parchment paper “sling.” Cut two strips of parchment paper to fit the width of the pan, leaving an overhang on two opposite sides. Lay them in the pan in a cross shape. This overhang will act as handles to lift the brownies out once they’ve cooled.

Step 2: Create the Wet Ingredient Base

1. Melt Butter and White Chocolate: In a medium, microwave-safe bowl, combine the 113g of unsalted butter and 170g of white chocolate. Microwave in 30-second intervals, stirring well after each interval, until the mixture is completely melted and smooth. Be careful not to overheat or the white chocolate can seize. Alternatively, you can use a double boiler by placing the bowl over a saucepan of simmering water.

2. Cool Slightly: Set the melted chocolate mixture aside to cool for about 5-10 minutes. It should be warm, not hot, to the touch. This prevents the eggs from scrambling when you add them.

Step 3: Combine and Whisk

1. Add Sugar and Eggs: Pour the 200g of granulated sugar into the slightly cooled white chocolate mixture and whisk until combined. Add the 2 room-temperature eggs and the 1 teaspoon of vanilla extract. Whisk vigorously for about 1 minute. The mixture should become glossy, pale, and slightly thickened. This step is key to developing the coveted shiny, crinkly brownie top.

Step 4: Incorporate the Dry Ingredients

1. Sift for Smoothness: In a separate small bowl, place a fine-mesh sieve over top. Add the 120g of all-purpose flour, 20g of matcha powder, and 1/2 teaspoon of salt. Sift the ingredients together into the bowl. Sifting is especially important for matcha powder, which is prone to clumping. This ensures an even distribution of flavor and a smooth, uniform green color.

2. Fold Gently: Add the sifted dry ingredients to the wet mixture. Using a rubber spatula, gently fold everything together until just combined. You should see a few faint streaks of flour remaining. Do not overmix. Overmixing develops the gluten in the flour, which will result in tough, cakey brownies instead of soft, fudgy ones.

3. Add Mix-ins (Optional): If you are using white chocolate chips or nuts, add them now and fold a few more times until they are evenly distributed.

Step 5: Bake to Perfection

1. Pour and Spread: Pour the batter into your prepared baking pan and use the spatula to spread it into an even layer, making sure it reaches all the corners.

2. Bake: Place the pan in the preheated oven and bake for 25-30 minutes. The edges should be set and slightly puffed, and the center should look just barely set (it will no longer be liquidy but will still be very soft).

3. The Doneness Test: To check for doneness, insert a toothpick or wooden skewer into the center of the brownies. Unlike a cake, you do not want it to come out clean. It should come out with moist, fudgy crumbs attached. If it comes out with wet, liquid batter, it needs a few more minutes. If it comes out clean, it is likely overbaked.

Step 6: The All-Important Cooling Process

1. Cool Completely: Remove the pan from the oven and place it on a wire cooling rack. Let the brownies cool completely in the pan, which will take at least 2 hours. This is the hardest but most crucial step. Cutting into them while warm will result in a gooey mess. As they cool, the brownies will set up, becoming even fudgier and developing a richer flavor.

2. Chill for Clean Cuts (Optional but Recommended): For ultra-clean, professional-looking squares, cover the cooled pan with plastic wrap and refrigerate for at least 1 hour (or up to 4) before slicing.

3. Slice and Serve: Once cooled (and chilled, if desired), use the parchment paper handles to lift the entire slab of brownies out of the pan. Place on a cutting board and use a large, sharp knife to slice into 16 squares. For the cleanest cuts, wipe the knife clean with a damp paper towel between each slice.