Gather your ingredients. Preheat the oven to 350 F with a rack in the center. Generously grease a 9 x 13-inch baking dish with unsalted butter or neutral oil (vegetable, canola, or safflower).

Add the eggs, coconut milk, 2 cups of milk (or milk mixture), and melted or softened butter to a blender. Blend until smooth and uniformly pale yellow. If the butter is softened and not melted, foamy chunks of butter will float to the top, and that's OK.

Add the sugar, glutinous rice flour, and miso, if using, and blend until smooth and thick. Scrape the sides and bottom of the blender bowl (when turned off) as needed with a rubber spatula.

Transfer the batter to the prepared baking dish. Sprinkle the shredded coconut evenly over the top of the butter mochi batter. If using, sprinkle the toasted sesame and sea salt flakes as well.

Bake until the top and sides are golden brown, and a toothpick or bamboo skewer inserted into the middle comes out clean, about 65 minutes.

Transfer the baking dish onto a wire rack and allow the butter mochi to cool for at least an hour before flipping it out of the dish. Slice into 24 to 36 even slices. If it is still warm, it will be gooey and harder to slice. Mochi cures over time, and butter mochi is stretchier, chewier, and even more enjoyable the nice day.

Store leftovers in an air tight container at room temperature for up to 3 days, but I doubt they will last that long!