Preheat your oven to 350 and spray the inside of an 8 oz. wide-mouth mason jar with nonstick spray (if you don’t have a jar you can certainly use an oven-safe ramekin, but make sure you watch it as it will likely bake faster).
Whisk together the sugar, yogurt, egg white and vanilla until smooth.
Fold in the flour, baking powder and salt until everything is combined. For the streusel, mix together the cubed butter pieces, brown sugar, cinnamon and flour and using your fingers work the butter into the dry ingredients until a fine crumb forms.
Pour half of the batter into the bottom of the jar, top with 1/3 of the streusel mixture, top with the remaining batter and then top the entire thing off with the remaining streusel mixture.
Place on a baking sheet lined with foil and bake at 350 for 20-25 minutes or until a toothpick inserted comes out clean.
Let cool before eating, and be careful…the jar will be hot! You can top it with a cream cheese frosting.