CAKE

1. Preheat oven to 325 degrees. Set aside a 10-inch tube pan. DO NOT GREASE OR FLOUR PAN.
2. Separate the eggs: In this recipe, you’re going to separate the eggs, then beat the egg whites. It’s always easier to separate eggs that are cold, and egg whites whip up with more volume at room temperature. Therefore, start by separating the 5 large eggs, straight from the fridge. Once they’re separated, set aside the egg yolks, in a small bowl. Then transfer the egg whites to the bowl of a stand mixer fitted with the whisk attachment and leave them to come to room temperature while you mix the other ingredients.
3. Measure the flour by the spoon and level method. In a large bowl, sift together the flour, baking powder, salt, and brown sugar. You can use a whisk. However, I sift it through a mesh wire strainer to make sure there are no small hard lumps of brown sugar.
4. Make a well in the center of the dry ingredients. Add the oil, egg yolks, water and vanilla. Mix until all ingredients are combined thoroughly and mixture is smooth. Set aside.
5. Add the cream of tartar to the bowl of egg whites on the stand mixer. Whisk the egg whites until they are shiny with stiff peaks, but not dry. This shouldn’t take more than a couple of minutes with a stand mixer, a little longer if using a hand mixer.  Pour the egg mixture slowly over the beaten egg whites, using a spatula to gently fold the egg mixture into the egg whites. Go down the sides and under the bottom of the mixture and back up the other side. Fold only until the two are incorporated. Try not to mix. 
6. Pour the batter into the tube pan, using a small offset spatula to evenly distribute the batter. If you see any air bubbles run a knife through them to pop them.
7. Bake the cake on the lowest oven rack until it’s golden brown on top and a toothpick test comes out clean, about 60 to 65 minutes. Immediately invert the cake onto a funnel or bottle and leave it until it’s completely cooled. 
8. Run a knife around the center tube and the insides of the pan and gently shake the pan to make sure the cake has loosened. Invert the cake onto a plate, then place a cake plate on top, flipping the cake over onto the cake plate. 

BUTTERSCOTCH FROSTING

1. Add the cream cheese to the bowl of a stand mixer and beat until the cream cheese is very smooth and free of any lumps. Add the butter and mix until light and creamy.
2. Add the brown sugar, (breaking up any small clumps), and beat until the mixture is very smooth and creamy. Make sure to beat long enough so that the brown sugar is no longer gritty. 
3. Sift in two cups of powdered sugar and add 2 tablespoons of heavy cream, and mix until combined and smooth. Sift in 1 1/2 cups more of powdered sugar, and add 2 more tablespoons of cream. Check the consistency, and add the remaining sugar and cream if needed for a perfect spreading consistency. Add the vanilla and salt and mix to incorporate. 
4. Frost the top and sides of the cake.