Preheat the oven to 350°F. Line a muffin pan with muffin liners. Melt the butter, you can do this in the microwave or in a small pot over the stovetop.
To make the topping: In a large mixing bowl, add the melted butter, cane sugar, light brown sugar, and flour.
Mix together until a paste like texture forms. Set aside.
To make the batter: In a large mixing bowl add the butter, light brown sugar, and cane sugar. Mix, using a hand mixer until the butter and sugars are completely combined with the butter.
Add the sweet potato puree and eggs and mix to combine completely.
Next, add in the dry ingredients: flour, baking powder, cinnamon, and salt and mix to combine into a smooth batter.
Fold in the blackberries.
Scoop batter into the muffin pan and fill three-quarters full. You’ll get 12 muffins.
Crumble the topping on top of the muffin batter.
Bake for 20 to 25 minutes, or until golden brown and done.
To make the glaze: In a large mixing bowl, add the powdered sugar, blackberry powder, and water.
Whisk together until a smooth glaze forms. If you want a thicker glaze, use less water if you want a thinner glaze you can use more water.
Once the muffins cool, drizzle the glaze on top.
Store in an airtight container for up to 3 days.