Prepare the fudge base: In a small saucepan, combine the sugar-free Irish cream, heavy cream, butter, and powdered erythritol. Heat over medium heat, stirring constantly, until the mixture begins to simmer. Reduce the heat to low and cook for 5-7 minutes, stirring frequently, until it thickens slightly.

Melt the chocolate: Remove the saucepan from the heat and stir in the chopped chocolate, vanilla extract, and salt. Continue stirring until the chocolate is completely melted and the mixture is smooth.

Set the fudge: Line a small square baking dish (about 8x8 inches) with parchment paper. Pour the fudge mixture into the dish, spreading it evenly. If you'd like, sprinkle cocoa powder or chopped nuts on top for added texture.

Chill the fudge: Refrigerate the fudge for at least 2-3 hours, or until it's firm enough to cut into squares.

Serve: Once set, lift the fudge out of the dish using the parchment paper. Cut into small squares and serve chilled or at room temperature.