Set your oven to 350°F (175°C) and let it warm up while you prepare the batter. Lightly grease a 9×9-inch baking dish with butter or nonstick spray and set it aside.

In a large mixing bowl, combine flour, brown sugar, cinnamon, and a pinch of sea salt. Cut in cold butter using a fork or pastry cutter until the mixture resembles large, buttery crumbs. Set aside for later.

In a separate bowl, whisk together flour, baking powder, sea salt, and cinnamon. Set this dry mix aside.

Using a stand mixer fitted with a paddle attachment (or a handheld mixer), beat softened butter and sugar on high speed for about 1 minute until light and fluffy. Add in the eggs and vanilla extract, mixing just until combined.

Next, gradually add the dry ingredients while beating at medium-high speed. Finally, mix in the sour cream until the batter is silky smooth.

Pour the cake batter into the greased baking dish, spreading it into an even layer. Generously sprinkle the crumb topping over the batter.

Bake for 40-45 minutes, or until the cake looks puffed, set, and a toothpick inserted in the center comes out clean. The top should be golden and slightly crisp!

Store any leftovers in an airtight container in the refrigerator for up to 5 days. For longer storage, freeze individual portions for up to 2 months—perfect for a quick breakfast treat!