Prepare pan: Line an 8x8 inch or 9x9 inch baking dish with parchment paper. This will make it easier to remove the fudge later.
Combine ingredients: In a large, microwave-safe bowl, combine the sweetened condensed milk, white chocolate chips, and butter.
Melt: Microwave in 30-second intervals, stirring after each interval, until the chocolate chips and butter are melted and the mixture is smooth. Be careful not to overheat the mixture, as this can cause it to seize.
Add flavor and color: Stir in the vanilla extract. Add the green food coloring, a few drops at a time, and stir until you achieve the desired vibrant green color. Gel food coloring is highly pigmented, so start with just a little and add more gradually.
Pour and chill: Pour the fudge mixture into the prepared baking dish and spread it evenly.
Add hearts: Immediately press the red heart sprinkles or candies into the fudge.
Chill: Cover the dish with plastic wrap and refrigerate for at least 2 hours, or preferably overnight, to allow the fudge to set completely.
Cut and serve: Once the fudge is set, use the parchment paper to lift it out of the baking dish. Cut the fudge into squares or other shapes as desired.