Line an 8×8-inch square pan with parchment paper, ensuring that the paper overhangs the edges.

In a saucepan over low heat, combine the semi-sweet chocolate chips and sweetened condensed milk. Stir continually until melted and smooth.

Pour the melted chocolate mixture into the prepared pan, spreading it evenly with a spatula.

Warm the raspberry jam in a small saucepan over low heat until it becomes pourable.

Drizzle the warm raspberry jam over the top of the fudge mixture and swirl it with a knife or skewer.

Refrigerate the mixture for at least 2 hours until firm to the touch.

Lift the fudge out of the pan using the parchment paper and slice into squares.