Prep the Pan: Generously butter or spray a 9×13‑inch baking pan to prevent sticking. :contentReference[oaicite:2]{index=2}

Make the Crumble Topping: In a bowl, combine the flour, brown sugar, cinnamon, and salt. Mash the soft butter into the mixture with a fork or fingers until crumbly; set aside. :contentReference[oaicite:3]{index=3}

Prepare the Cinnamon Sugar Layer: In a small bowl, whisk together sugar, flour, and cinnamon until well mixed; set aside. :contentReference[oaicite:4]{index=4}

Mix Dry Cake Batter: In a large bowl, combine flour, sugar, baking powder, baking soda, and salt. :contentReference[oaicite:5]{index=5}

Add Butter: Add the soft butter to the dry mixture and beat on medium‑low until it resembles moist sand. :contentReference[oaicite:6]{index=6}

Combine Wet Ingredients: In another bowl, whisk together sour cream, milk, eggs, and vanilla until smooth. :contentReference[oaicite:7]{index=7}

Make Batter: Pour the wet ingredients into the dry mixture and beat until mostly smooth. :contentReference[oaicite:8]{index=8}

Assemble Cake: Spread half of the batter into the pan, sprinkle the cinnamon‑sugar layer over it, then spread remaining batter over the top. Finally, sprinkle the prepared crumble evenly across the cake. :contentReference[oaicite:9]{index=9}

Bake: Preheat oven to 350°F (175°C) and bake the assembled cake about 55 minutes, until a toothpick in the center comes out clean. :contentReference[oaicite:10]{index=10}

Cool: Let the cake cool completely on a wire rack before slicing and serving. :contentReference[oaicite:11]{index=11}