Preheat the oven to 350°F (180°C) with a rack in the center. Grease and line a 9 x 13-inch baking pan with parchment paper.

In a saucepan, heat the butter over medium heat until brown bits form and the butter is lightly brown, a few minutes. Remove from heat and cool to about 110°F. Pour the butter into a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment.

In a microwave-safe bowl, melt the chocolate in 30-second bursts. Do not overheat the chocolate or it will become thick and muddy.

Add the melted chocolate to the butter and mix (by hand or with the mixer) until incorporated. Add the sugar and mix to combine. Add the eggs, mixing after each one, and then add the two milks and vanilla extract. Mix well until homogenous.

Find a large bowl and mix together the dry ingredients (mochiko, baking powder, cocoa powder, tapioca starch). Add the wet ingredients to the bowl and fold in the dry ingredients. Then grab a whisk and mix everything until well-combined and smooth. Don't be shy, you don't want clumps or a lumpy batter.

Pour everything into the prepared pan and bake for 60 to 70 minutes (depending on your oven), until an inserted toothpick or skewer comes out clean. It is normal for the top to crack close to the end of baking, and for the center to dome up a bit. Once cooled, the cake will level off naturally and deflate a bit.

I like my butter mochi without any toppings or glaze, but if you'd like to add a pop of red and an extra kick of spice, try this glaze.

Mix the confectioners' sugar with the melted butter and gochujang until smooth. You want a thick but "drippy" glaze, so if it's not runny enough, drizzle in a little milk and mix until smooth.

Optionally mix in a drop or two of red food coloring to the glaze. The top of our butter mochi has a red sheen because I brushed on a thin layer of red glaze.

Spread the glaze evenly over the still warm butter mochi and allow to set. Optionally mix in a drop or two of red food coloring to the glaze.

Top the butter mochi with the optional toppings as desired.

Slice, serve, and enjoy!