In the bowl of a stand mixer fitted with the paddle attachment beat butter at medium speed for 30 seconds until smooth. Add the sugar and beat until fluffy and light.
Add vanilla extract and egg. Beat on high speed for 30 seconds. Scrape sides and bottom of the bowl as needed.
Sift flour, cocoa powder, baking powder, salt, and espresso powder together in a medium bowl.
On low speed, slowly mix the flour mixture into the wet ingredients until combined.
Divide the dough into two parts and roll each portion out to 1/4 inch thickness on a piece of parchment paper. Stack, put onto a baking sheet, and refrigerate for at least 1 hour or overnight (cover top with parchment).
Preheat oven to 375°F (180°C). Line two baking sheets with parchment.
Take out one part of the dough and cut into heart shapes using a cookie cutter. Transfer the cookies to the prepared baking sheet then using a smaller heart-shaped cookie cutter, cut smaller hearts into the centers of half of the hearts. Remove the smaller hearts and re-roll the remaining dough. Continue cutting until all the dough is used.
Bake for 10 minutes, until the edges are firm, the cookies will still appear soft. Rotate the baking sheet halfway through bake time. Allow to cool on baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
Repeat with remaining chilled dough.
When the cookies are cooled completely, spread Nutella over whole hearts then place cookies with heart cut centers over tops. Decorate with sprinkles. Store in an airtight container.