(the following is adjusted from what I tested with corrections I think will help)

ingredients

for the butter mochi

• 8 oz mochiko sweet rice flour

• 1-1/2 tsp baking powder

• 1/2 tsp kosher salt

• 1/2 cup granulated sugar

• 1-1/2 cup milk, warmed

• 4 tbsp coconut oil, melted

• 1 egg

• 1/2 tbsp vanilla extract 

for the streusel topping

• 1/2 cup all-purpose flour

• 1/4 cup granulated sugar

• 2 tbsp brown sugar

• 2 tbsp coconut oil, melted and cooled

• 1 tsp cinnamon

steps

1. Preheat oven to 350F.

2. In a medium mixing bowl, add mochiko, baking powder, kosher salt, sugar. Whisk until thoroughly combined.

3. In a heatproof bowl, add milk and coconut oil. Microwave for 30s until warm but not hot.

4. Pour the milk and coconut oil into a small mixing bowl, whisk together until frothy. Let it cool a little bit so it doesn't cook the egg. Add in vanilla extract and egg - whisk well. 

5. Pour the wet ingredients into the dry ingredients. Mix well until combined.

6. Pour the batter into a 9x9 (or close to that size) pan with walls. Bake for 30 minutes.

7. While baking, make the streusel. Add the flour, sugars, and cinnamon into a small mixing bowl. Whisk well.

8. Melt the coconut oil in a small heatproof bowl (~30s in microwave). Pour it into the small mixing bowl and mix until combined.

9. Add the streusel topping to the butter mochi. Bake for another 15 minutes until streusel is browned.

10. Let cool before slicing and serving. Enjoy!