Line an 8x8-inch square baking pan with parchment paper or foil. Set aside
Place the chocolate into a large microwave-safe bowl, and heat in 30 second intervals, stirring after each one, until melted and smooth.
Stir in the condensed milk and vanilla until combined. The mixture will be slightly thick.
For the White Chocolate Fudge
Place the chocolate into a large microwave-safe bowl, and heat in 20 second intervals, stirring after each one, until melted and smooth.
Stir in the condensed milk and vanilla until combined.
Alternating between the two mixtures, spoon into the prepared pan. Using a toothpick or knife, run through them both to create swirls.
Refrigerate for at least 2 - 4 hours or overnight until completely set.
Video
Notes
This fudge can be stored in an airtight container at room temperature for 1 week, or in the fridge for 2 - 3 weeks. It also freezes well for up to 2 months. Thaw overnight in the fridge before serving.