Makes about 25 truffles. In a metal bowl set over a pan of barely simmering water, melt the chocolate, stirring until it is smooth. Remove the bowl from the pan and let the chocolate cool slightly. In a bowl whisk together the chevre, powdered sugar, vanilla, and lemon extract until the mixture is light and fluffy. Whisk in the chocolate until the mixture is combined well and chill the mixture, covered, for 1 hour, or until firm. Form heaping teaspoons of the mixture into balls and roll the balls in the cocoa powder. Chill the truffles on a baking sheet lined with waxed paper for 30 minutes. You can also roll in chopped nuts or coconut for variety. The truffles keep in an airtight container, chilled, for 3 days.