Preheat oven to 300 F. In heatproof bowl over saucepan of hot (not boiling) water, melt chocolate, stirring occasionally. Remove from heat and let cool. Meanwhile, in bowl, beat butter with sugar until fluffy. Stir in chocolate and vanilla. Add flour and salt; stir until blended. Mix in chopped crystallized ginger. Divide into 4 equal parts and chill 2 hours or until firm. Turn onto lightly floured work surface and roll out to 1/4″ thickness. Cut with cookie cutters and place cookies on baking sheets lined with parchment paper. Bake 30 minutes or until firm to the touch. Remove from oven and let cool for 2 minutes, then remove to wire racks to cool completely. Store in an airtight container at room temperature.