Step 1

Heat the oven. Arrange a rack in the middle of the oven and heat the oven to 350°F. Coat a 9x13-inch baking pan with butter or oil. Melt 1 stick unsalted butter in the microwave or on the stovetop.

Step 2

Prepare the dry and wet ingredients. Place 1 pound mochiko, 2 cups granulated sugar, 2 teaspoons baking powder, and 1/2 teaspoon kosher salt in a large bowl and whisk to combine. Place 2 cups milk, 4 large eggs, and 2 teaspoons vanilla extract in a medium bowl and whisk to combine.

Step 3

Combine the dry and wet ingredients. Pour the wet ingredients into the dry ingredients and, with a wooden spoon, stir until well combined. Add the melted butter and 1 can coconut milk and mix until fully incorporated and smooth.

Step 4

Pour into the baking pan and top with coconut. Pour the mixture into the prepared pan and rap the pan on the counter a couple of times to bring any air bubbles up to the surface. Evenly sprinkle 1/2 cup shredded coconut on top of the mixture, a handful at a time, being careful not to jiggle the pan too much, as you want the coconut to stay on the top. Then sprinkle on a few pinches of flaky salt, if desired.

Step 5

Bake the mochi for about 1 hour. Bake until the mochi is set and golden brown on top, 60 to 70 minutes.

Step 6

Cool before cutting and serving. Set the pan on a wire rack and let cool completely, about 1 hour. Slice into rectangles, using a plastic knife to minimize sticking; I cut four columns and five rows to make twenty 2 1/4 by 2 1/2-inch pieces. If the knife seems to be sticking, rub it with a little unsalted butter or neutral oil.