Preheat the oven to 350 degrees F. Line a baking sheet with foil. Butter and flour a 9-inch springform pan and place it on the baking sheet. Set aside.
Make the Cinnamon Sugar Layer
Whisk together the sugar, cinnamon, and salt. Set aside.
Make the Streusel
Whisk together the sugar, flour, cinnamon, and salt. Then, mix in the melted butter. Set aside.
Make the Cake
In a bowl, whisk together the flour, baking powder, and salt.
In a large bowl, cream together the butter and sugar until they are light and creamy, 2 to 3 minutes.
Add the eggs, oil, and vanilla extract and mix until well combined.
Add 1/3 of the dry ingredients to the wet and mix just until combined.
Mix in 1/2 of the milk.
Continue with another 1/3 of the dry ingredient, then the rest of the milk, and finally the last of the dry ingredients.
Pour half of the cake batter into the prepared pan. Sprinkle the cinnamon sugar evenly over the batter. Spoon the rest of the batter in and carefully spread it out.
Crumble the streusel over the top of the cake.
Bake the cake in the springform pan on the baking sheet for 50 to 60 minutes or until a toothpick comes out with just a few moist crumbs.
Allow the cake to cool for 10 minutes. Then, run a knife around the edges before releasing the cake. Cool for another 2 hours before slicing.
Notes
Notes:
When you pull the cake out of the oven, you'll notice little puddles of butter on top. Don't worry! That's how it's supposed to look. The butter will soak down into the cake making it extra moist and flavorful and the streusel topping will still be nice and crunchy.
Allow the cake to fully cool for the cleanest cuts.
Storage:
Store the cake in an airtight container. It will keep for 2 days at room temperature and up to a week in the fridge.