Preheat your oven to 350 degrees F, and liberally grease a 9x13-inch baking pan with baking spray.
In the bowl of your stand mixer fitted with the whisk attachment, beat the egg whites on high speed until stiff peaks form.
Transfer the whipped egg whites to a small bowl and place in the refrigerator.
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 and bottom of the bowl as needed.
Add the sweet potatoes, hot water, and vanilla extract, and beat for another 3 to 4 minutes.
Turn your mixer down to its lowest speed and carefully add the flour, baking powder, cinnamon, cloves, salt, baking soda, and nutmeg. Mix the batter until just combined. (Be careful not to overmix.)
Remove the egg whites from the refrigerator and gently fold them into the batter.
Pour 1/2 of the batter into the prepared pan. Cover with 1/2 of the streusel. Repeat with the remaining batter and streusel.
Bake for 55 to 65 minutes, or until a toothpick inserted into the center of the cake comes out moist but mostly clean.
Let cool in the pan for 10 minutes, then poke the top of the cake in various locations with a toothpick.
Lightly cover the cake with foil or plastic wrap so it does not dry out. While the cake continues to cool, prepare the sauce.