Preheat oven to 350°F (175°C). Lightly grease or line an 8×8-inch baking pan with parchment paper.

In a large mixing bowl, whisk together mochiko flour, sugar, matcha powder, and salt.

In a small saucepan, melt white chocolate and butter together over low heat. Stir constantly until smooth. Let cool for 2–3 minutes.

Whisk eggs, coconut milk, and vanilla into the chocolate mixture.

Pour the wet mixture into the dry ingredients. Stir until smooth and lump-free.

Pour batter into the prepared pan and smooth the top with a spatula.

Bake for 45–50 minutes, or until the edges are lightly golden and a toothpick inserted in the center comes out mostly clean.

Let the cake cool completely before slicing into 9 squares.

Serve warm or at room temperature. Store leftovers in an airtight container.