Preheat your oven to 350°F (175°C). Grease an 8x8-inch baking pan with butter for easy removal.

In a large mixing bowl, combine the glutinous rice flour, granulated sugar, baking powder and pumpkin pie spice. Set aside

In another large mixing bowl, combine melted butter, coconut milk, milk, pumpkin puree, eggs, and vanilla extract. Add the wet ingredients into the dry ingredients then whisk until smooth and well-combined. The batter should be thick but slightly runny.

Bake for 55-65 minutes or until the mochi is set and a toothpick inserted into the center comes out clean.

Let the mochi cool completely in the pan, about 1 hour, so the mochi firms up. Once cool, use a knife or spatula to loosen the edges, then flip onto a cutting board. Using a knife, cut the mochi into small squares or rectangles. You can optionally dust with powdered sugar on top.