Line an 8×8-inch square pan with parchment, leaving an overhang on two sides for easy removal.

Chop the dark chocolate into small, even pieces and set aside in a heatproof bowl.

In a small saucepan, combine the sweetened condensed milk and butter over low heat until the butter melts, about 3-4 minutes.

Pour the hot condensed milk mixture over the chopped dark chocolate and let sit undisturbed for 1 minute.

Stir slowly until completely smooth and thick; add vanilla and salt, stirring to incorporate.

Pour the chocolate mixture into the prepared pan and smooth the top, then tap the pan to settle.

Chill the fudge in the refrigerator for at least 2 hours or until firm. For best slicing, chill overnight.

Melt the white chocolate until smooth and, if too thick, add up to 1 teaspoon vegetable oil to loosen.

Pipe V-shaped fangs onto parchment and let set until firm, about 10-20 minutes at room temperature.

Prepare the 'blood' drizzle by warming raspberry jam slightly and mixing in corn syrup if desired.

Slice the chilled fudge into squares, wiping the knife clean between cuts for a sharp edge.

Top each square with two white chocolate fangs and drizzle with the red gel or jam.

Return to the fridge for 10 minutes to set the drizzle if necessary.

Serve chilled or at cool room temperature for best texture.