Preheat oven to 350F and line a cupcake tin with cupcake liners.
In a medium-sized bowl, whisk together the flour, baking soda, salt, and chai spice mix. Set aside.
In a medium-sized bowl or the bowl of a stand mixer fitted with the paddle attachment, beat the butter and oil together on medium-high speed until completely combined. This will only happen if the butter is fully at room temperature. About 2-3 minutes.
With the mixer on low speed, stream in the granulated sugar then beat on medium speed until combined and fluffy.
Add the eggs, one at a time, mixing well on low speed in between each addition, scraping down the sides and bottom of the bowl as necessary. Add the vanilla extract and mix on low-medium speed until combined.
With the mixer on low, add half of the dry ingredients. Once almost fully incorporated, add half of the milk and mix until almost combined. Repeat this with the other halves of the dry ingredients and the milk. Do not over mix.
Divide the batter evenly amongst the cupcake cups. The batter should be the perfect amount for 12 regular-sized cupcakes. Fill the liners until they are ½ - ¾ of the way full.
Bake the cupcakes for 15-17 minutes until a toothpick inserted into the center of the cupcake comes out clean. Let cool in the pan for 5 minutes, then transfer to a cooling rack to cool completely.