Preheat your oven to 170ºC (340ºF) and line two 8-inch baking pans with parchment paper.

In a large mixing bowl, sift together all-purpose flour, cornstarch, ground cardamom, cinnamon, ginger, allspice, nutmeg, baking powder, baking soda, and salt.

In a stand mixer, cream together the softened butter, granulated sugar, and dark brown sugar until light and fluffy (about 3-4 minutes).

Gradually add eggs to the creamed mixture, mixing on low speed until fully combined (about 2 minutes).

With the mixer on low, gently add half of the dry mixture, then add sour cream, vegetable oil, and vanilla extract, followed by the remaining dry mixture until just mixed.

Pour the batter into prepared pans and bake for 28-30 minutes until golden brown and springy.

Remove from oven and cool in pans for 10 minutes before inverting onto a wire rack to cool completely.

To make the frosting, beat softened butter and both sugars until smooth, then add cream cheese and vanilla bean paste and mix until light and fluffy (3-5 minutes).

Once cooled, level the cakes, place one layer on a serving plate, and spread frosting on top. Add the second layer and cover the cake with a thin layer of frosting.

Decorate your Chai Cake as desired and serve with a warm cup of chai or coffee.