In a large mixing bowl, combine mascarpone cheese, heavy cream, powdered sugar, and vanilla extract. Beat mixture on medium speed until soft peaks form (3-5 minutes).

In a separate bowl, mix cooled espresso and coffee liqueur (if using). Dip each crushed chocolate wafer cookie into the coffee mixture briefly, ensuring they are soaked but not falling apart.

Gently fold the soaked cookie crumbs into the mascarpone mixture until well combined.

Cover bowl and refrigerate for at least 2 hours or until mixture is firm enough to handle.

Once chilled, use a small cookie scoop or hands to form bite-sized balls. Place truffles on a parchment-lined baking sheet.

Melt the chopped semi-sweet chocolate in a microwave-safe bowl in 30-second intervals, stirring until smooth.

Dip each truffle into the melted chocolate, allowing excess chocolate to drip off, then place back on the parchment paper.

While chocolate is still wet, dust the tops of the truffles with cocoa powder.

Refrigerate the truffles for at least 30 minutes to set the chocolate.