Butter mochi is Hawaii’s version of a blondie. It’s slightly chewy and mildly sweet, almost like a cross between vanilla cake and traditional Japanese mochi. It’s also incredibly easy to make. Just stir together and bake!
Preheat the oven to 350°F (180°C). Grease a 9x13 inch (23x33 cm) baking pan with butter or oil, or alternatively line the pan with parchment paper with overhang on the sides. This will allow you to transfer the butter mochi to a cutting board after baking for easier cutting.
In a mixing bowl, use a wooden spoon to combine the melted butter and sugar. Add the eggs, one at a time, and combine until smooth. Stir in the coconut milk, evaporated milk, and vanilla extract. Finally add the mochiko flour and baking powder and whisk until completely smooth and lump-free.
Pour the mixture into the prepared pan. Gently rap it on the counter a couple times to release any trapped air bubbles, then transfer to the oven and bake for about 1 hour or until it is set and the top is golden brown.
Cool to room temperature before slicing. If you've lined the pan with parchment paper, use the overhang to carefully remove the entire slab to a large cutting board. Cut into 5 rows crosswise and 4 rows lengthwise to yield 20 squares. If your knife starts to stick, rub it with a little oil to get smoother cuts of butter mochi. Store leftover squares in an airtight container at room temperature for up to 3 days.
Don’t be afraid of overmixing. Mochiko flour is gluten-free so there is no concern as you would have when baking with flour of yielding a tough product by overmixing.
When slicing into squares, if your knife starts to stick, rub it with a little oil to get smoother cuts of butter mochi.