Butter a large baking sheet (10-by 12-inches) with 1 tablespoon of the butter, and set aside.
In a 2-quart saucepan over low-heat, add the remaining butter, sugar, water, coarsely chopped walnuts, liqueur, and lemon juice. Cook, stirring occasionally to dissolve the sugar, until the mixture reaches the soft-crack stage, or 270 degrees F.
Pour the candy onto the buttered sheet pan and evenly sprinkle the chocolate chips over the top. As the chocolate melts, spread them evenly over the top of the candy with a rubber spatula. Sprinkle the finely chopped walnuts over the chocolate, and let the candy cool before breaking into uneven pieces.