Preheat oven to 325 °F. Line muffin tin with paper liners or grease.
In a medium bowl, combined cake flour, all-purpose flour, cocoa powder, sea salt, and baking soda. Sift all dry ingredients together and set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream butter. Once smooth, add brown sugar and mix until incorporated. Add eggs one at time on low speed. Scrape down sides of bowl as needed.
On low speed, add the flour mixture in three additions, alternating with sour cream. Mix on low speed until combined.
In another bowl, whisk together vanilla, brewed espresso, and espresso powder. Add to batter slowly until incorporated.
Divide batter between cupcake liners, filling each cup about ¾ full. Bake in preheated oven for 20-25 minutes until a toothpick inserted in center of cake comes out clean. Remove cupcakes from tin and allow to cool on wire racks. Once cooled to room temperature, cupcakes are ready for frosting.