Put the butter and chocolate in a heatproof medium bowl and place the bowl over a pan of barely simmering water. Stir until the chocolate has melted and the mixture is smooth, about 6 minutes. Stir in the coffee until smooth. Add the walnuts,hazelnut, biscotti pieces and orange liquor, and stir until combined. Cover the bowl and refrigerate until firm but moldable, 1 1/2 to 2 hours.