Prepare the pan: Line an 8×8-inch baking pan with parchment paper, leaving some overhang for easy removal.
Melt the chocolate: Add the white chocolate chips, sweetened condensed milk, and butter to a saucepan. Heat over low heat, stirring constantly until smooth and completely melted.
Add the flavor: Remove from the heat and stir in the green tea powder, vanilla extract, and salt until evenly combined and smooth.
Pour into the pan: Transfer the mixture to the prepared pan and spread it into an even layer.
Chill: Refrigerate for at least 2 hours, or until the fudge is firm.
Slice: Lift the fudge from the pan using the parchment paper and cut into 16 squares.
Serve: Serve chilled or let the pieces sit at room temperature for a few minutes before serving.