In a food processor chop fine the apricots and hazelnuts and mix in enough of the liqueur to hold the mixture together. Shape the mixture into 1-inch balls, roll the balls lightly in the sugar, and let them stand at room temperature, uncovered, for 24 hours.
In the top of a double boiler set over barely simmering water, melt the chocolate, stirring occasionally, until it is smooth and remove it from the heat. Coat half of each ball with the chocolate, letting the excess drip off and wiping the underside of the ball gently against the side of the double boiler. Chill the balls on a baking sheet lined with a piece of parchment paper until the chocolate has hardened.
The confections keep, chilled, in an airtight container for up to 2 weeks.