Preheat oven to 350°F. Grease an 8×8-inch baking pan or line it with parchment paper.
In another medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, ginger, nutmeg, and kosher salt until well combined.
2 cups All-purpose flour, 2 tsp Baking powder, 1/2 tsp Baking soda, 1/2 tsp Kosher salt, 1 1/2 tsp Ground cinnamon, 1/4 tsp Ground ginger, 1/4 tsp Ground nutmeg, 1/8 tsp Ground cloves
In a large bowl, whisk the granulated sugar and melted butter until combined. Add the eggs one at a time, mixing well after each one. Whisk in the mashed sweet potato and vanilla extract. Add half the dry ingredients, stirring to combine. Gradually stir in the buttermilk, then add the remaining dry ingredients, mixing until well combined.
1/3 cup Unsalted butter, 1/2 cup Granulated sugar, 2 large Eggs, 1 cup Mashed sweet potato, 1 tsp Vanilla extract, 1/2 cup Full-fat buttermilk
Pour the batter into the prepared pan and spread it out evenly. Sprinkle the refrigerated streusel evenly over the top. Bake for 40-50 minutes until golden brown and a toothpick inserted into the center comes out clean. Remove to a wire rack to cool for at least 30 minutes before serving.