Lightly spray an 8 or 9 inch pan square pan with non-stick cooking spray and make sure it is well covered. Bring water to a boil in microwave, about 1 minute. Add gelatin and stir well. Return to microwave for 1 minute and stir well. (This step ensures that Jello is completely dissolved.) Add marshmallows and return to microwave for 45 seconds to 1 minute or until marshmallows are puffed and slightly melted. Whisk until marshmallows are completely dissolved. Creamy layer will float to the top. Pour into prepared pan. Refrigerate 45 minutes or until well set- they should be very firm and easy to handle. Loosen edges with a knife. Starting at one end, roll up tightly. With seam side down, cut into 10-12 (1/2) inch slices. We found it easiest to cut with a piece of thread or dental floss. Just put the string around roll-up, cross and pull. Serve immediately or refrigerate until ready to serve.