In a microwave-safe bowl, combine the dark chocolate chips with the sweetened condensed milk. Microwave the mixture in 20-second intervals, stirring after each interval. Continue until the chocolate is melted and the mixture is smooth, which should take about 1 minute in total.
After achieving a smooth consistency, add the peppermint extract and mix thoroughly to infuse the chocolate with refreshing mint flavor.
Allow the bowl to cool for approximately 10 minutes at room temperature, letting the mixture firm up slightly.
Once the mixture has cooled, gently fold in the crushed graham crackers and walnuts, ensuring they are well incorporated throughout.
With slightly damp hands (to prevent sticking), take out small portions of the mixture, approximately one tablespoon each, and roll them into smooth balls.
Arrange the rolled truffles on a parchment-lined baking tray for easy handling.
After all the truffles are rolled, carefully coat each one in the blue sparkling sugar, rolling them gently to ensure they are generously covered.
To finish, sprinkle a few sea salt flakes atop each truffle; this will create a picturesque contrast and enhance flavor.
Place the tray in the refrigerator and chill the truffles for at least 1 hour, or until they are firm enough to hold their shape.
Notes
Arrange the truffles in festive boxes or on a decorative plate. For an extra whimsical touch, dust more sparkling sugar around them to create a playful, winter wonderland effect.