Line an 8x8-inch pyrex pan with foil hanging over the sides.
PREPARE THE 1st LAYER:
In a large microwave-safe bowl, combine the 3 cups semisweet chocolate chips, 1 cup white chocolate chips and butter. Microwave at 1 minute intervals, stirring after each, until melted and smooth.
Whisk in the powdered sugar and Kahlua until the mixture is smooth. Place the mixture in the prepared pan, and lay a sheet of plastic wrap over the top; press and smooth the top down.
PREPARE THE 2nd LAYER:
In a medium microwave-safe bowl, melt 1 cup of white chocolate chips and ½ cup of the semisweet chocolate chips (at 30-second intervals) until smooth. Then beat in the butter and Kahlua until smooth. Remove the plastic wrap from the 1st layer and pour the 2nd layer on top. Smooth the top with a rubber spatula. Refrigerate until firm.
Notes
TIPS:
Short burst in the microwave with stirring prevent scorching.
Using foil to line the pan makes slicing MUCH easier.
Cold, refrigerated fudge slices cleanly with minimal smudging.
Use a sharp, hot knife. Dip the knife in hot water, wipe dry, and slice for perfect edges.
How to Store Kahlua Fudge: Store in the refrigerator in an airtight container for up to 1 week. To freeze, wrap tightly and freeze up to 2 months. Thaw in the refrigerator before serving.