Pre-heat your oven to 350F.
Prepare a 9x13 inch baking dish by spraying it with non-stick spray. To make the cake: In the bowl of your mixer, sift together flour, sugar, baking soda, baking powder and salt.
Add in butter, a few pieces at the time and mix until you are left with crumbles.
Add in eggs, vanilla and buttermilk and beat until the mixture is combined, making sure to scrape down the sides of the bowl.
To make the filling: combine 1 cup light brown sugar with 1 and 1/2 tablespoons ground cinnamon.
Pour half of the batter into the prepared pan. The batter is going to be thick, so it will take a bit of effort to spread it. Sprinkle the filling on top of the batter.
Pour remaining batter on top. Use a small knife to make swirls in the cake to give it a marbled look.
To make the topping: whisk together flour, cinnamon, sugar, and vanilla. Cut in butter using two forks until it’s crumbly (you can also use your mixer to do this). Sprinkle the crumb topping evenly over the batter.
Bake for 45-50 minutes, or until the cake has set.