In the top of a double boiler or in a microwave oven on medium, stirring often, heat chocolate, coarsely chopped, water, freshly brewed coffee or milk and pinch of salt (optional) just until the chocolate is melted and smooth.
Remove from heat. With a rubber spatula, stir in unsalted butter 2 or 3 pieces at a time, cut into small pieces.
Continue to stir (do not beat) until perfectly smooth. Stir in 1 to 2 tablespoons liqueur (optional)
For a pourable glaze, let stand at room temperature, stirring occasionally, until the mixture cools to 90°F. For frosting, let stand until spreadable. If the frosting becomes too stiff, set the pan in a larger pan of hot water and stir gently with rubber spatula; or remelt and cool to 90°F to use as a glaze. This keeps for up to 3 days at room temperature, or up to 3 weeks refrigerated. Or freeze for up to 6 months. Soften or melt before using.