A scrumptious brunch cake featuring mashed sweet potato with a crisp streusel topping.
Preheat the oven to 350°F. Coat a 9-by-13-inch baking pan with nonstick baking spray. Set aside.
In a medium bowl, using an electric mixer on medium speed, beat the flour, butter, granulated and brown sugars, cinnamon, and salt together until the butter is well incorporated and the topping looks like wet sand. Set aside. (See note)
In a small bowl, combine the brown sugar and cinnamon. Set aside. (See note.)
In a large bowl, using the mixer on medium speed, beat the granulated sugar, mashed sweet potatoes, oil, and vanilla together until well combined. Add the eggs and beat until they are worked into the batter. Scrape down the sides and bottom of the bowl.
In another medium bowl, stir together the flour, baking powder, cinnamon, salt, nutmeg, and ginger.
Add the dry ingredients and evaporated milk to the sweet potato (wet) mixture in the large bowl in multiple additions, alternating back and forth between the two, starting and ending with the flour mixture and beating on medium speed. Scrape down the sides and bottom of the bowl and stir in any unmixed bits of batter with a spatula.
Spread half the batter in the prepared baking pan with a spatula. Sprinkle the cinnamon sugar on top of the batter, evenly distributing it. Add the rest of the batter on top of the cinnamon-sugar layer. Use a spatula to spread out the batter. Sprinkle the crumb topping on top of the batter, evenly distributing it.
Bake until a toothpick inserted into the center comes out clean, 44 to 49 minutes. (See note)
For the streusel - instead of mixing with an electric mixer, you can combine with a fork and then mix with your hands.
The cinnamon-sugar layer in the middle is nice but in my view, the cake is sufficiently sweet and delicious without it.
Baking cake - If you have an instant read thermometer and prefer a more exact way to test for whether the cake is done, the internal temperature should be 210 degrees F.