Line an 8-inch square baking pan with parchment paper, leaving an overhang on two sides to form a sling. Lightly grease the parchment if it tends to stick.

Fill a small saucepan with 1–2 inches of water and bring it to a gentle simmer. Place a heat-safe bowl over the saucepan, ensuring the bottom of the bowl does not touch the water.

Add the white chocolate chips, sweetened condensed milk, and butter pieces to the bowl. Stir slowly and constantly over low heat until the mixture is smooth and glossy with no visible chips. If the mixture seems too thick, stir in 1–2 teaspoons of heavy cream or whole milk to loosen it slightly.

Remove the bowl from the heat. Stir in the vanilla extract, 1 teaspoon orange extract, orange zest (if using), and salt. Taste carefully while warm and add up to an additional 1/2 teaspoon orange extract if you prefer a stronger citrus flavor.

Pour about two-thirds of the warm fudge mixture into a second bowl and set aside; this will be the vanilla base layer. Leave the remaining one-third in the original bowl for the orange swirl layer.

To the smaller portion in the original bowl, add a drop or two of orange gel food coloring. Stir well, adding more gel a tiny bit at a time until you reach a soft creamsicle orange shade.

Pour the larger, uncolored vanilla mixture into the prepared pan. Use a spatula to spread it into an even layer, then tap the pan gently on the counter to release any air bubbles.

Spoon the orange-colored mixture over the vanilla layer in small dollops. For a layered look, gently spread the orange mixture across the top into a mostly even second layer. For a swirled look, drag a butter knife or skewer through both layers, swirling gently without overmixing so you keep distinct orange and vanilla areas.

Cover the pan lightly with foil and refrigerate for at least 2–3 hours, or until the fudge is completely firm. For the cleanest slices, chill 4 hours or overnight.

Use the parchment sling to lift the fudge out of the pan and place it on a cutting board. With a sharp knife, cut into 1–1 1/2 inch squares, wiping the blade clean between cuts for neat edges. Serve slightly chilled or at cool room temperature.