Preheat oven to 350 degrees F (if using a silver spring form pan, or 325 degrees F if using a dark nonstick spring form pan). Lightly grease pan.
In a mixing bowl, combine crushed cookies and the butter and mix well. Press onto the bottom of spring form pan and set aside.
In a large mixing bowl with an electric mixer, combine cream cheese, sugar, and vanilla and beat until light and creamy. Add the flour to the cream cheese mixture and beat until smooth. Add the melted chocolate and sour cream and mix well. Add the eggs, 1 at a time, mixing on low speed after each addition until just blended. Gently fold in Junior Mint pieces.
Pour the batter into prepared pan. Cover bottom of pan with foil to prevent water from seeping in and place in a shallow water bath. Bake for 1 hour to 1 hour and 10 minutes, until the center is almost set. Run a sharp knife around the rim of the pan and allow cake to cool on a wire rack before removing rim of pan. Refrigerate at least 4 hours or overnight before serving. Cheesecake may be made up to 2 days in advance before serving and will keep for up to 1 week in the refrigerator.