Beat cheese until light and fluffy. Add 0.75 cup sugar and beat again. Add eggs one at a time; beating after each. Add sour cream. Mix well. Add remaining sugar to melted chocolate. Mix one cup of cheese mixture into chocolate. Pour cheese mixture into pan. Drop spoonfuls of chocolate mixture onto top and swirl with knife. Bake at 220ºC or 15 minutes with a pan of water on the bottom rack of oven. Reduce temp to 250 and bake 1 hour longer. Run knife around edge of cake. Cool. Top as desired. Variation: Use semi-sweet mint chocolate chips and add entire 1 cup of sugar at one time.