Preheat your oven to 170ºC (340ºF) and prepare two 8-inch round baking pans by lining them with parchment paper.

In a large mixing bowl, sift together the all-purpose flour, cornstarch, ground spices, baking powder, baking soda, and salt. Set aside.

In a stand mixer, combine room temperature butter with both granulated and dark brown sugars and beat on medium speed for about 3 minutes until light and fluffy.

Add the eggs one at a time, mixing well after each addition until fully incorporated.

Gently add half of the dry ingredients to the creamed mixture, followed by the sour cream, vegetable oil, and vanilla extract. Mix until smooth, then add remaining dry ingredients.

Divide the batter evenly between the prepared pans and bake for 28-30 minutes or until a toothpick comes out clean.

Let the cakes cool in the pans for 5 minutes, then transfer to a wire rack to cool completely.

Prepare the frosting by creaming together softened butter, powdered sugar, and brown sugar until smooth, then add cream cheese and vanilla bean paste.

Once the cakes are completely cooled, level the tops if needed and frost between the layers and around the cake as desired.