Preheat your oven to 350ºF (175ºC) to make sure it's ready for baking. Grease a 9 by 13 inch baking pan thoroughly to prevent sticking, then set it aside. I always make sure to coat the corners well so the mochi lifts out easily after baking.

In a large mixing bowl, combine the sweet rice flour, granulated sugar, baking powder, and salt. Mix these dry ingredients together until they're evenly distributed and there are no lumps.

In a separate bowl, whisk together the coconut milk, evaporated milk, melted butter, eggs, and vanilla extract until the mixture is smooth and everything is fully incorporated.

Pour the wet ingredients from Step 3 into the bowl with the dry ingredients from Step 2. Stir gently but thoroughly until you have a smooth, lump-free batter. Scrape the sides and bottom of the bowl as needed to ensure all flour is incorporated.

Pour the prepared batter into the greased baking pan from Step 1. Gently tap the pan on a flat surface a few times to help release any air bubbles that may have formed in the batter.

Place the pan in your preheated oven and bake for about 1 hour, or until the top and edges turn golden brown. Every oven bakes a bit differently—I like to start checking for doneness at 55 minutes by inserting a toothpick into the center; it should come out mostly clean.

Remove the pan from the oven and let the Butter Mochi cool completely in the pan before cutting it into squares. Cooling fully helps the mochi set and gives cleaner slices. Serve at room temperature and enjoy. Store any leftovers in an airtight container for 3 to 4 days at room temperature, a week in the fridge, or freeze for longer storage.