In a small nonstick pan over medium-low heat, add the sesame seeds and stir occasionally. Toast until the sesame seeds are fragrant, then remove from the heat and let cool.

In a medium bowl, combine the flour, salt and baking powder.

In a blender (countertop or immersion) or food processor, add the sugar and black sesame seeds, then blend until it looks like damp sand and there are no sesame seeds visible.

Add the sesame and sugar mixture to the dry ingredients, and mix until combined.

Add the eggs, vanilla, butter and milk to the dry ingredients and mix until combined.

Grease an 8 by 8 inch pan, then pour in the mochi. Bake at 350F for 30 minutes, or until a toothpick inserted into the center of the mochi comes out clean. Cool completely before cutting into squares and serving.

The mochi can be stored in an airtight container for up to 3 days. It can also be stored in the refrigerator for up to 1 week, or in the freezer for up to 1 month. If you refrigerate the mochi, make sure you microwave or toast it before eating. If you freeze the mochi, you can defrost and eat at room temperature or heat it up.