Preheat oven to 350°F (175°C). Grease and line two 8-inch round cake pans with parchment paper.

In a medium bowl, whisk together flour, baking powder, and salt. Set aside.

In a large bowl, beat butter and sugar until light and fluffy, about 3–4 minutes. Add eggs one at a time, beating well after each addition. Mix in vanilla.

Alternately add the flour mixture and milk to the butter mixture, beginning and ending with flour. Mix until just combined.

Divide batter evenly between prepared pans. Smooth tops and bake for 22–25 minutes, or until a toothpick inserted in the center comes out clean.

Let cakes cool in pans for 10 minutes, then transfer to a wire rack to cool completely.

While cakes cool, prepare espresso syrup: mix cooled espresso with sugar until dissolved. Set aside.

Make the mascarpone filling: In a large bowl, whip heavy cream until stiff peaks form. In another bowl, beat mascarpone, powdered sugar, and vanilla until smooth. Gently fold whipped cream into mascarpone mixture.

Level cakes if needed. Brush the top of each cake layer generously with espresso syrup.

Place one cake layer on a serving plate. Spread half of the mascarpone filling over the top. Add the second layer and spread remaining filling over the top and sides.

Dust top with cocoa powder using a fine-mesh sieve. Garnish with chocolate shavings if desired. Chill for at least 2 hours before serving.