Preheat oven to 350°F. Line a 9x13” pan with foil or parchment paper and spray with nonstick cooking spray.
Make the streusel: in a medium bowl, whisk flour, brown sugar, granulated sugar, and cinnamon. Slowly add melted butter and whisk until crumbs are formed. The mixture will look wet, but it’s supposed to look that way.
In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites on high speed until stiff peaks form. Transfer the egg whites to a small bowl and chill until ready to use.
Clean your stand mixer bowl and switch to the paddle attachment. Beat the granulated sugar and oil on medium-high speed until combined. Add the egg yolks 1 at a time, combining well after each addition and scraping down the sides of the bowl as needed. Add the mashed sweet potatoes, hot water, and vanilla and beat for another 3-4 minutes.
Turn your mixer to it’s lowest speed and carefully add the flour, baking powder, cinnamon, cloves, salt, baking soda, and nutmeg. Mix until the batter is just combined, being careful not to over mix. Remove the egg whites from the refrigerator and gently fold them in using a spatula or wooden spoon.
Pour half the batter into the prepared pan. Top with half the streusel. Repeat with remaining batter and streusel. Bake for 55-65 minutes until a toothpick comes out moist but mostly clean. Let cool in the pan. Serve warm or room temperature. Store tightly covered at room temperature for up to 3 days.