Preheat oven to 350°. Grease and flour a bunt baking pan. Put sweet potatoes in a bowl and blend until mostly mashed and soft. Add the remaining ingredients, except for the chocolate chips. Mix on medium power for two minutes. Add the chocolate chips and fold into the batter. Pour the cake mixture into the bunt pan. Bake in the center of the oven for 60 minutes. For extra chocolate flavor, melt 1/2 cup of the chocolate chips in a double boiler, or microwave on low until melted. Pour over the cooled cake as a drizzle.