1. Pour coffee into a wide bowl or pie plate and set aside.
2. In a large bowl, beat whipping cream on medium speed until frothy. Increase speed to high and whip until stiff peaks form. Set aside.
3. In a separate large bowl, beat mascarpone on medium speed until smooth and light. Reduce speed to low and add sugar and vanilla. Beat until thoroughly combined, then increase speed to medium and mix until smooth.
4. Using a spatula, gently fold one-third of the whipped cream into the mascarpone to lighten the mixture. Add remaining whipped cream and gently fold until no white streaks remain.

Assemble Trifle

1. Quickly dip a biscuit into the coffee and place the cookie standing on its side in the trifle dish. Continue doing this until a single layer is formed, breaking or trimming cookies as needed.
2. Spread one-third of the mascarpone mixture over the biscuit layer. Dust with cocoa powder using a fine-mesh sieve.
3. Repeat the steps of layering the savoiardi biscuits, mascarpone, and cocoa powder two more times.
4. Cover with plastic wrap and refrigerate for at least 8 hours before serving.