Line an 8‑inch square baking pan with parchment paper, leaving an overhang on two opposite sides to help lift the fudge out later. Lightly spray the parchment with nonstick spray if desired. Crease the parchment at the edges so it fits snugly in the pan for neat corners.

In a medium saucepan, add the semisweet chocolate chips, 1 tablespoon unsalted butter, 1 cup sweetened condensed milk, instant espresso powder or coffee granules, vanilla, and a pinch of fine sea salt.

Place the saucepan over low heat. Stir slowly and steadily until the chocolate is melted and the mixture is smooth and glossy, 3–5 minutes. Do not walk away; the mixture can scorch. The fudge base is ready when it is thick but pourable and pulls away from the sides of the pan as you stir.

Carefully taste a small amount and adjust the coffee level if desired by stirring in up to an additional 1/2 teaspoon espresso powder. Pour the chocolate coffee mixture into the prepared pan and spread it into an even layer. Tap the pan gently on the counter to remove air bubbles, then let the layer rest at room temperature for about 10 minutes, until it loses most of its surface shine but is not fully firm.

In a clean saucepan (or wipe out the first one), add the white chocolate chips, 2 tablespoons unsalted butter, remaining sweetened condensed milk (about 4 oz), instant espresso powder, vanilla, and a pinch of fine sea salt.

Warm the cappuccino mixture over low heat, stirring constantly, until the white chocolate chips are fully melted and the mixture is smooth. Keep the heat low; white chocolate can seize if overheated. If the mixture seems too thick to pour, remove it from the heat and stir in 1–2 tablespoons extra sweetened condensed milk or heavy cream until pourable.

Taste and adjust the coffee intensity in the cappuccino layer. It should be slightly lighter than the bottom layer, like a foamy cappuccino. Add up to an additional 1/2 teaspoon espresso powder if desired and stir well.

When the chocolate coffee layer has set slightly, pour the warm cappuccino fudge mixture evenly over the top. Use a spatula to spread it to the edges. For a marbled look, drag a butter knife through both layers in gentle figure‑eight motions to create mocha swirls.

If desired, lightly sprinkle the top with espresso powder or cocoa powder and/or finely chopped chocolate‑covered espresso beans.

Cover the pan loosely with foil or plastic wrap. Refrigerate for at least 2 hours, or until the fudge is firm enough to slice. For the neatest squares and best texture, chill overnight.

Once firm, lift the fudge out of the pan using the parchment overhang and place it on a cutting board. Use a long, sharp knife to cut into 1–1 1/2‑inch squares, wiping the blade with a warm, damp cloth between cuts for clean edges. Serve, store, or package for gifting as desired.