Make the coffee soak: Brew strong coffee or espresso and let it cool. If using, stir in coffee liqueur. Set aside in a shallow dish.
Whip the cream: In a large bowl, beat cold heavy cream with powdered sugar and vanilla until you get soft-to-medium peaks.
Beat the mascarpone: In another bowl, briefly beat mascarpone with a pinch of salt until smooth.
Don’t overmix.
Fold together: Gently fold the whipped cream into the mascarpone in two additions. Stop when it’s smooth and fluffy.
Add Biscoff spread: Microwave the spread for 10–15 seconds to loosen. Fold 1/2 cup into the cream mixture until just combined.
Dip the cookies: Quickly dip each Biscoff cookie into the cooled coffee—1 to 2 seconds per side.
They should be lightly soaked, not soggy.
Layer it up: Arrange a single layer of dipped cookies in an 8x8-inch (20x20 cm) dish. Spread half the cream mixture over the top.
Repeat: Add a second layer of dipped cookies, then the remaining cream.
Finish and chill: Drizzle a little warmed Biscoff spread over the top and swirl. Cover and chill for at least 4 hours, ideally overnight.
Garnish and serve: Just before serving, dust with cocoa powder or sprinkle crushed Biscoff cookies.
Slice and enjoy.