Preheat your oven to 350°F (175°C). This ensures that your cake bakes evenly.
In a large mixing bowl, cream together the 5 tablespoons of unsalted butter and 1 cup of granulated sugar until light and fluffy. This should take about 2-3 minutes with an electric mixer.
Beat in the large egg, followed by the 1 cup of sour cream and 2 teaspoons of vanilla extract. Mix until well combined.
In a separate bowl, whisk together the 3 cups of all-purpose flour, 1 teaspoon of baking powder, 1 teaspoon of baking soda, 1 teaspoon of sea salt, and 1 teaspoon of ground cinnamon.
Gradually add the dry ingredients to the wet mixture, mixing just until combined. Be careful not to overmix, as this can lead to a dense cake.
In another bowl, combine the 16 ounces of cream cheese with 1 cup of granulated sugar and 1 teaspoon of vanilla extract. Beat until smooth and creamy. Add the large egg and mix until just combined.
Pour half of the cake batter into the prepared 9x13 inch baking pan. Spread it evenly across the bottom. Next, carefully dollop the cream cheese filling over the batter, spreading it gently to cover as much surface area as possible. Pour the remaining batter on top, smoothing it out to cover the filling.
In a small bowl, combine the 1 cup of lightly packed brown sugar, 1 tablespoon of unsalted butter, and 1 teaspoon of ground cinnamon. Use a fork to mix until crumbly. Sprinkle this topping generously over the cake.
Bake in the preheated oven for 45-50 minutes, or until a toothpick inserted into the center comes out clean. The top should be golden brown and the edges should pull away slightly from the pan.
Allow the cake to cool in the pan on a wire rack for at least 20 minutes before slicing. For an extra touch, drizzle with a simple icing made from 1 cup of powdered sugar, 1 tablespoon of melted butter, 1 tablespoon of milk, and 1 teaspoon of vanilla extract.
