Mix the condensed milk and butter together.

Stove: Cook the mixture in a medium saucepan over medium heat, stirring constantly, until the bottom of the pan starts to show when you scrape it with your wood spoon. The candy mixture should be thick enough to show you the bottom of the pan for a couple of seconds before the mixture levels out again.

Microwave: Pour mixture into a deep microwaveable bowl. If 900 watts, let cook on full power for about 6 minutes — removing and stirring at least every 2 minutes, or until thick enough to be rolled (remember that when it cools down, mixture will be thicker). While it is cooking, do not leave the microwave unattended because mixture will rise and possibly bubble over, making a mess. Every time it rises, pause until mixture settles back down. If 1100 watts, cook at 80 % power. Double batches take more time to cook.

When it is ready, mix in the vanilla extract and the food coloring, and then spread the mixture onto a greased plate. Let cool to room temperature before starting to roll the candy mixture around each grape, molding into balls with greased hands. Then, dredge each candy gently in the granulated sugar until totally covered, and place into paper bonbon cups.

The candies can be stored in an airtight container at room temperature for up to 2 days. The mixture can be also stored, covered well, in the refrigerator for up to 4 days, brought to room temperature, and rolled into balls with the grapes.