Use fresh, good-quality matcha for the brightest color and flavor. Avoid overbaking to keep a fudgy texture—look for moist crumbs on the tester. Store airtight at room temperature for up to 3 days, or refrigerate for up to 5 days. For clean slices, chill briefly before cutting. You can melt the butter and chocolate on the stovetop over low heat, stirring constantly.