Preheat your oven to 350°F (175°C) and prepare a standard cupcake tin by lining it with cupcake liners.

In a small bowl, combine your chai spices to create a harmonious blend of flavors. Set aside 3 teaspoons for the cupcake batter and reserve 1 1/4 teaspoons for the frosting.

In a medium mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, 3 teaspoons of the chai spice mix, and a pinch of salt.

In another bowl, whisk together the milk and sourdough discard until smooth and fully combined.

Using a stand mixer, mix the unsalted butter and granulated sugar until light and fluffy, about 4-5 minutes. Add in the eggs one at a time, followed by the sour cream and vanilla extract.

Gradually add the dry ingredients to the wet mixture, alternating with the milk mixture, until combined without overmixing.

Spoon the batter into cupcake liners, filling each about three-quarters full to allow room for rising. Bake for 16 to 17 minutes, or until a toothpick comes out clean.

Let the cupcakes cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.

In a mixing bowl, beat the softened butter and powdered sugar until smooth and creamy. Gradually blend in reserved chai spice mix, vanilla extract, and heavy cream as needed for consistency.

Once cupcakes are completely cool, frost generously with chai-spiced buttercream, decorating as desired.