Finely chop the chocolate and place in a bowl. Over a medium heat, warm the heavy cream until just before it comes to the boil. Stir in the instant coffee until dissolved. Pour over chocolate and let stand for 30 minutes until melted. Whisk until smooth and shiny. Stir in vanilla extract. Cover bowl with plastic wrap and refrigerate overnight. Roll rounded teaspoons of chocolate mixture into balls and roll in pecans. Wrap, refrigerate and then enjoy.