Preheat oven to 350°F (conventional) and line a 9x9" baking pan with parchment paper.
In a large bowl, mix sugar, melted butter, oil, and vanilla for 2 minutes using a hand whisk.
Add eggs and egg white, and whisk for another minute.
Sift in cake flour, salt, baking powder, and baking soda. Gently fold with a rubber spatula until combined.
Add sour cream and hot brewed coffee, and fold until smooth batter forms. Do not overmix.
Pour half of the batter into the prepared pan. Sprinkle half of the coffee streusel on top.
Spoon the remaining batter over the streusel, spread it out gently, and top with the rest of the streusel.
Bake for 30-35 minutes until a toothpick comes out with moist crumbs.
Let the cake cool in the pan for 15 minutes before removing it.