Spray a 9x5 baking dish with nonstick spray and set aside.

Combine the butter, pinch of salt, and orange zest in a medium pot. Place over medium-low heat and stir gently until butter is melted.

Whisk the condensed milk and 2/3 cup cocoa powder into the pot until completely combined; mixture will resemble brownie batter.

Keep heat on medium-low. Use a spatula to stir gently but CONSTANTLY (seriously, CONSTANTLY --don't let the chocolate burn on the bottom) until mixture has thickened and is pulling away from the sides of the pot, about 8-10 minutes.

Remove pot from heat. Use the spatula to turn out the truffle mixture into the prepared baking dish and smooth into a thin, even(ish) layer. You want this to cool quickly, not look pretty.

Refrigerate the truffle mixture for around 4 hours, or until you're ready to scoop and form the truffles.

Assemble little bowls with your desired toppings -- the extra cocoa powder, sprinkles, or sanding sugar mentioned up above; you could also use chopped nuts, toasted coconut, or coookie crumbles. Be creative!

Remove the cold truffle mixture from the fridge. Scoop out a scant tablespoon of the mixture and roll between your hands to form a smooth ball.

Roll the truffle in your toppings and place on a platter or a muffin liner until ready to serve. Keep refrigerated if not being served right away.