Melt chocolate and butter together. This can be done in the microwave, in short bursts, or on a double boiler on the stove. Do NOT let any water in the mix, or it will seize - turn solid.
Mix until chocolate and butter are well-combined.
Beat egg yolk and stir in.
Add spices and alcohol (if adding). Mix well.
Put aside until cool and firm enough to handle, but still soft.
Use a large spoon to scoop out enough to sit in a teaspoon. Use your hands - they will get messily chocolatey (and you'll have to lick it off afterwards, oh the woe) - to create roughly round balls.
Pop each made truffle into a shallow bowl of cocoa, wattleseed, or Spicy Fruit Sprinkle.
Toss until the truffle is relatively dry on the surface.
Refrigerate until solid.
Serve, if desired, in small decorative cases.