Preheat oven to 350ºF. Prepare a 9-inch springform pan with baking spray that contains flour.
In a medium bowl whisk the flour, baking powder, and kosher salt together. Set aside.
2 cups All-purpose flour, 2 tsp Baking powder, 1 tsp Ground cinnamon, 1/4 tsp Ground ginger, 1/4 tsp Ground nutmeg, 1/2 tsp Kosher salt
In a large mixing bowl cream the butter, granulated sugar, and brown sugar until light and fluffy. Add the egg and vanilla extract and beat until combined.
1/2 cup Unsalted butter, 1/2 cup Granulated sugar, 1/4 cup Dark brown sugar, 1 large Egg, 1 tsp Vanilla extract
Stir the flour mixture into the wet batter in thirds, alternating with the buttermilk just until some dry flour remains. Fold in the grated carrots.
1/2 cup Buttermilk (full fat), 2 cups Grated carrots
Spread the batter evenly into the prepared pan, and sprinkle the frozen streusel over the top. Bake for 40-50 minutes until a toothpick inserted into the center comes out clean. Let cool completely before adding the glaze.