In the bowl of a stand mixer fitted with the paddle attachment, add the sweetened condensed milk, powdered sugar, butter, cocoa powder and peppermint extract.
Mix on low until combined, scrape down the sides of the bowl as needed to ensure everything is combined. Transfer the bowl to the fridge and allow it to chill for about an hour, or until you can easily scoop out the filling.
Line two baking sheets with parchment paper. Using a tablespoon, measure out the filling onto the baking sheets. You’ll get about 35 candies. You’re just measuring the filling here, it’s okay if it’s still a bit sticky.
Place the trays in the freezer and let them chill for 20 minutes, or until they are firm enough to handle with your hands (not too sticky).
Remove from freezer and form them into the iconic squares, by squishing each side together with your index finger and thumb. Place them back on the parchment paper and place the baking sheets in the freezer until the squares are very firm, at least 1 hour.
Add the milk chocolate and white chocolate into separate heatproof mixing bowls and melt. You can melt using a double boiler, or doing 30 second intervals in the microwave, stirring between each one.
If you want to color the candies pink, green, and yellow like Fannie May then divide the white chocolate into 3 bowls. Add a small amount of beet powder for pink, matcha powder for green, and the India Tree Nature’s Colors for yellow to make pastel colors. Stir to combine completely.
Remove the candies from the freezer and dip into the milk chocolate and white chocolate. I like to use a fork, like a spoon, so excess chocolate can drip back into the bowl, then place back on the baking sheets. To get the iconic swirl that’s on top, once the candies sit for a moment, take a small amount of chocolate and swirl it on top.
Place the tray back in the freezer to set until firm, about 20 minutes.