Heat chocolates, butter and milk in a pan until chocolates and butter are partially melted. Remove from heat and stir until completely melted. Whisk in desired flavoring until creamy-smooth.
Transfer to a bowl and let stand until firm enough to hold its shape, about 2 hours.
Using a tablespoon (a spring-action 1 Tb. scoop is ideal), mold chocolate into balls, 1 level Tb. at a time, and place on a cookie sheet lined with greased parchment paper.
Place desired coating in a small bowl. Working one at a time, drop truffles into the bowl with greased fingertips. Shake bowl back and forth so truffles are completely coated. If necessary, roll truffles by hand to make round. Return to parchment. (Can be refrigerated in an airtight container up to 5 days or frozen up to 1 month.) Before serving, let stand at room temperature to soften slightly.