Butter mochi is a Hawaiian cake that is sweet and gooey, not unlike like Japanese mochi. Rice flour is a core pantry ingredient in most Japanese households, including mine, so I almost always have the ingredients on hand to whip up this cake when the mood (or need) strikes. Just like this recipe, I’m a little bit Japanese and a little bit American. The combination of American ingredients like butter and evaporated milk with Japanese ingredients like rice flour and sesame seeds feels familiar and comforting to me. Butter mochi can be baked plain or topped with coconut and black and white sesame seeds or slices of fruit like strawberries, mango or peaches. You can serve butter mochi with ice cream if you like as well.
Preheat the oven to 350 degrees F (175 degrees C). Grease an 8-inch-square cake pan or 10-1/2-by-7-inch cake pan with butter.
Put the 4 tablespoons butter in a medium saucepan and cook over medium heat until melted. Meanwhile, whisk the coconut milk to remove any lumps. Add the coconut milk to the melted butter and reduce the heat to low. Gently warm the mixture, stirring often, until just above room temperature and no lumps remain.
Whisk together the mochiko, sugar, baking powder and sea salt in a large bowl.
Whisk together the eggs, evaporated milk and vanilla in a medium bowl. Pour this mixture into the dry ingredients and stir until just combined. Add the melted butter-coconut milk mixture, whisking continuously, until fully incorporated and smooth with no lumps.
Pour the batter into the prepared pan and tap the pan on the counter a few times to remove any air bubbles. Evenly sprinkle the top with the coconut chips or flakes. Sprinkle with the black and white sesame seeds and finish with the fleur de sel.
Bake the mochi until it is set and golden brown on top, 1 hour 5 minutes to 1 hour 15 minutes. You can bake the mochi longer for a firmer texture, or for less time for a gooier texture. If using a glass or dark metal pan, subtract a few minutes from your baking time.
Transfer the pan to a wire rack to cool completely. Coat a knife with butter and cut around the edges to help the cake separate from the pan and prevent the cake from sticking to the knife. Serve the cake directly from the pan.