Spread chocolate hazelnut spread between pairs of ladyfinger biscuits to make 8 sandwiches.
Briefly dip each sandwich in cooled coffee. Do not oversoak.
Whip the mascarpone, cold heavy cream, powdered sugar, and vanilla until thick and smooth.
Cover each biscuit sandwich with mascarpone cream and shape into a large oval coffee bean.
Make a groove down the center of each dessert using a spoon or spatula.
Freeze for 45–60 minutes until firm enough to coat.
Melt the dark chocolate with coconut oil and allow it to cool slightly.
Coat the chilled desserts with melted chocolate and lightly dust with cocoa powder.
Refrigerate until the chocolate sets. Keep chilled until serving.