Preheat your oven to 325°F. Lightly grease a 9x13-inch metal baking pan with nonstick spray. Line the bottom with parchment paper for easy removal, then spray the parchment as well. If the parchment won’t stay down, clip it with metal binder clips.

In a medium bowl, whisk together the cake flour, baking powder, salt, and cinnamon until well combined. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and granulated sugar on medium-high speed for about 5 minutes, or until the mixture is very light and fluffy. Scrape down the bowl as needed.

Turn the mixer to low and add the egg whites one at a time, mixing for at least 30 seconds between each addition and scraping down the sides to ensure everything is evenly combined.

Add in the sour cream and vanilla extract, mixing just until combined. The batter might look slightly curdled at this point—don’t worry, it will come together.

With the mixer on low, alternate adding the dry ingredients and the buttermilk: start with ⅓ of the dry ingredients, then ½ the buttermilk, another ⅓ of dry, the rest of the buttermilk, and finish with the last of the dry ingredients. Mix each addition just until incorporated—do not overmix.

Pour the batter into your prepared pan and use an offset spatula or the back of a spoon to smooth the top evenly all the way to the edges.

In a small bowl, whisk together the brown sugar, flour, and cinnamon. Pour in the melted butter and stir until a thick, gritty paste forms.

Drop small spoonfuls of the cinnamon mixture evenly over the top of the cake batter. Use a knife, skewer, or toothpick to gently swirl the mixture through the batter, creating ribbons and pockets of cinnamon sugar. It’s okay if some of it stays in chunks—it’ll bake into gooey cinnamon pockets.

Bake the cake for 38–40 minutes, or until a toothpick inserted in the center comes out with just a few moist crumbs. Avoid overbaking so the cake stays soft and tender.

Let the cake cool completely in the pan on a wire rack before frosting.

In a medium saucepan, combine the granulated sugar, water, and corn syrup. Stir gently just to combine, then place over medium heat and bring to a boil.

Once boiling, do not stir. Let the sugar cook undisturbed until it begins to caramelize. First the bubbles will be fast and small, but they’ll slow and grow as the sugar starts to turn golden.

Watch closely once the mixture turns a deep amber color—it can burn quickly.

While the caramel cooks, warm the cream in the microwave for 1 minute so it’s ready to use.

When the caramel reaches your desired color, immediately remove the pan from heat and carefully whisk in the warm cream (it will bubble up vigorously!).

Stir in the vanilla, salt, and butter until smooth and glossy. Let the caramel cool slightly before using.

In the bowl of a stand mixer, beat the butter and cream cheese together on medium speed for 2 minutes. Scrape down the sides and bottom of the bowl, then beat again for 2 more minutes to get it super smooth.

With the mixer on low, slowly add the powdered sugar. Once combined, add the heavy cream, vanilla bean paste, and a pinch of salt.

Increase the speed to medium-high and beat for 3–5 minutes, or until light and fluffy.

Use a rubber spatula or wooden spoon to manually stir the frosting at the end—this helps press out any air bubbles and gives you that bakery-smooth look.

Once the cake is completely cooled, spread the cream cheese frosting evenly over the top. You can leave it in the pan

Spoon about half of the caramel sauce over the frosted cake and gently swirl it in with the back of a spoon.

Serve the remaining caramel on the side with each slice.

Store leftovers tightly covered at room temperature for 1 day or in the fridge for up to 4 days.