Prepare the Chai Spice Mix: Combine the cinnamon, ginger, cardamom, and allspice in a small bowl and whisk until evenly blended. The finished mixture will provide the chai spice needed for the cupcakes, buttercream, and optional garnish.
Steep the Chai Milk: Heat the whole milk until hot, either by bringing it to a boil or microwaving it for 1–2 minutes. Pour the hot milk over the chai tea bag and let it steep for 20–30 minutes. Remove the tea bag and allow the chai milk to reach room temperature before using it in the batter. The chai milk can also be prepared a day ahead and refrigerated overnight. Prepare the Oven and Pans: Preheat the oven to 350°F (177°C). Line a 12-cup muffin pan with cupcake liners, then place 2–3 additional liners in a second pan because the recipe makes approximately 14–15 cupcakes.
Combine the Dry Ingredients: Whisk together the cake flour, 3½ teaspoons chai spice mix, baking powder, baking soda, and salt until evenly distributed. Set the mixture aside.
Cream the Butter and Sugar: Using a handheld or stand mixer fitted with a whisk attachment, beat the softened butter and granulated sugar on high speed for about 2 minutes, until the mixture is smooth and creamy. Scrape down the sides and bottom of the bowl with a rubber spatula as needed. Add the Egg Whites: Beat the egg whites into the butter mixture on high speed for about 2 minutes, or until combined.
Add the Wet Ingredients: Beat in the sour cream or plain yogurt and vanilla extract until incorporated, scraping the bowl as needed.
Finish the Batter: Reduce the mixer to low speed and gradually add the dry ingredients, mixing only until they are incorporated. With the mixer still on low, slowly pour in the chai milk and mix just until combined. Do not overmix. The finished batter should be slightly thick. Fill the Liners: Spoon or pour the batter evenly into the cupcake liners, filling each only about two-thirds full to prevent the batter from spilling over the sides during baking.
Bake the Cupcakes: Bake at 350°F (177°C) for 20–22 minutes, or until a toothpick inserted into the center comes out clean. For approximately 35 mini cupcakes, use the same oven temperature and bake for about 11–13 minutes.
Cool Completely: Transfer the baked cupcakes to cool completely before applying the frosting.
Prepare the Buttercream: Using a handheld or stand mixer fitted with a paddle attachment, beat the softened butter on medium speed for about 2 minutes, until creamy.
Add the Frosting Ingredients: Stop the mixer and add 5½ cups (660g) confectioners’ sugar, the heavy cream, 1¾ teaspoons chai spice mix, vanilla extract, and a pinch of salt.
Whip the Frosting: Beat on low speed for 30 seconds, then increase to high speed and continue beating for 2 minutes. If the frosting appears curdled or greasy, beat in additional confectioners’ sugar as needed, using up to ½ cup (60g) more. If it is too thick to pipe or spread, add another tablespoon (15ml) of cream. If it tastes too sweet, add another pinch of salt. Frost the Cupcakes: Pipe the chai buttercream onto the completely cooled cupcakes. A Wilton 8B piping tip can be used for the frosting design.
Garnish and Serve: Finish the cupcakes with cinnamon sticks if desired, along with a sprinkle made from the remaining chai spice mix and a pinch of granulated sugar.
Store the Cupcakes: Cover leftover frosted cupcakes and refrigerate for up to 5 days.
