Combine milk, optional sugar, salt in small saucepan. Cook over medium heat, whisking a few times to dissolve sugar and scald milk.
Pour hot milk over the chocolate all at once. Rotate the bowl so the chocolate is completely submerged. Cover the bowl with a plate and let stand, undisturbed for 3-4 minutes.
Whisk slowly from the center out only until ganache is smooth and glossy. If the chocolate is not completely melted, place the bowl over a water bath; stir until melted.
To test the final consistency: A properly made truffle ganache is firm enough to shape and still taste creamy. Refrigerate a small amount of ganache 10 to 15 minutes. After chilling, the ganache should be firm. Adjust as necessary with more liquid or melted chocolate.
Stir the vanilla and olive oil into the ganache. Pour ganache into a shallow dish at room temperature for 30 minutes to firm. The ganache sets evenly in a 9-inch/23-cm glass pie pan or similar.
Refrigerate uncovered until the surface is no longer soft, then place a piece of parchment paper or plastic wrap directly onto the surface of the ganache, covering it completely Refrigerate 4 hours or until very firm. At this point, the ganache can be refrigerated for up to 1 week in an airtight container or frozen for a month.
Make the Truffle Centers:
Line a shallow container with parchment. Remove ganache from refrigerator. Use a spoon to scoop out 1-inch/2.5-cm pieces of ganache, and another to push the ganache off the spoon into the container. If you prefer more uniform truffles, use a 1⁄2-tbsp scoop. When a half dozen or so are made, roll and press the pieces into irregularly shaped rounds. Repeat until all the ganache has been used. If at any time the ganache becomes too soft to shape, refrigerate until cold and proceed. Cover and refrigerate the truffle centers in layers separated by parchment paper for 20 to 30 minutes before finishing with the cocoa coating. Alternatively, cut the truffle ganache into squares.
Finish the Truffles:
Roll in cocoa powder with sea salt, ginger, or other spice, nuts, seeds, coconut, cake crumbs
Refrigerate to set, 15 to 30 minutes. Serve at room temperature, sprinkled with a few grains of flaked sea salt.