Preheat oven to 350 degrees and line 12 standard muffin tin cups with paper liners.
Sift together flour, cocoa powder, baking soda, and salt into a medium bowl. Set aside.
In a large bowl, using an electric mixer on medium speed, beat the butter and sugar until smoothly blended and lightened in color, about 1 minute, scraping down the sides of the bowl as necessary. Add the eggs on at a time, beating until each is blended into the batter and it looks creamy, about 1 minute. Mix in the vanilla and espresso powder. On low speed, add half of the flour mixture until just incorporated. Mix in buttermilk and blend in. Mix in the remaining flour mixture until it is incorporated and the batter looks smooth.
Pour batter evenly into prepared muffin tin and bake for about 25 minutes. Cool 15 minutes in pan then remove cupcakes to wire rack to cool completely before frosting.
Raspberry-Peach Champagne Frosting
In a medium bowl, using an electric mixer on medium speed, beat the butter until smooth and creamy. Add the sugar, vanilla, and salt. Beat on low speed until just combined. Increase mixer speed and beat until smooth. Add milk or cream and beat until light and fluffy, 3-4 minutes. Fold in a spoonful or jam, adding more to taste.
Spoon frosting into a pastry bag fitted with a large tip of your choice. Pipe frosting onto each cooled cupcake.
Note: if you want a smoother frosting, use a seedless jam or strain your jam through a fine sieve to remove chunks or pulp.