In a medium bowl, whisk together the flour, baking powder, salt, and espresso powder. Set aside.
Using a hand or stand mixer, beat the softened butter and granulated sugar together on medium high speed until light and fluffy. Set a timer for 2-3 minutes, stopping halfway to scrape down the sides and bottom of the bowl.
Beat in one egg at a time, mixing well after each addition. Scrape down the bowl, then add the vanilla extract and mix until fully combined.
Stop using the mixer. With a spatula, gently fold in half of the flour mixture and half of the buttermilk by hand until just combined. Add the remaining flour mixture and buttermilk, folding again until everything is fully incorporated. Be sure to scrape the bottom of the bowl, but do not over mix, this keeps the cupcakes light and fluffy.
Divide the batter evenly among the 12 liners.
Place the pan in the preheated oven on the middle rack and bake for 15-16 minutes, or until a toothpick inserted into the center comes out clean.
Let the cupcakes cool in the pan for 2 minutes, then transfer them to a wire rack before soaking.