Step 1: Line an 8x8 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal. Set aside.
Step 2: In a large microwave-safe bowl, melt the 3 cups of milk chocolate chips. Microwave in 30-second intervals, stirring well after each, until completely smooth and melted. Be careful not to scorch the chocolate.
Step 3: Allow the melted chocolate to cool slightly (about 5 minutes), then gently fold in the 8 oz of thawed Cool Whip using a rubber spatula. Mix until no white streaks remain and the mixture is light and uniformly chocolatey. Do not overmix, as this can deflate the nougat.
Step 4: Pour the chocolate-Cool Whip mixture into the prepared baking pan. Spread it evenly to create a flat layer. Place the pan in the refrigerator and chill for at least 1 hour, or until the nougat layer is firm to the touch.
Step 5: Once the nougat layer is firm, melt the 10 oz of almond bark or chocolate coating in a separate microwave-safe bowl according to package directions. Microwave in 30-second intervals, stirring until smooth.
Step 6: Pour the melted almond bark evenly over the chilled nougat layer. Gently tilt the pan to ensure the entire top surface is coated.
Step 7: Return the pan to the refrigerator and chill for another 1 hour, or until the chocolate coating is completely set and firm.
Step 8: Once completely set, use the parchment paper overhangs to lift the slab of candy out of the pan. Place it on a cutting board. Warm a sharp knife under hot water, dry it, and then cut the large slab into desired bar sizes (typically 12-16 bars). Clean the knife between cuts for a smooth finish.
Step 9: Store the homemade 3 Musketeers bars in an airtight container in the refrigerator and enjoy!