Prepare the Baking Dish: Line a 9×9-inch baking dish with parchment paper, ensuring the paper extends up all four sides. Lightly spray the parchment paper with nonstick cooking spray to prevent sticking. Set aside while you prepare the fudge mixture.
Mix Flavoring and Color: In a small glass bowl, combine the banana flavoring and yellow food color gel. Stir well to create a uniform mixture that will give your fudge its distinctive banana flavor and appealing yellow color. Set aside for later use.
Melt the Base Ingredients: Add the butter, half and half, heavy cream, and clear vanilla flavoring to a 3 to 4-quart heavy-bottomed saucepan over medium heat. Stir continuously until the butter melts completely, creating a smooth mixture.
Add Sugar and Simmer: Add the sugar to the saucepan and stir constantly as the mixture comes to a simmer, which should take approximately 6 to 7 minutes. Continue stirring and allow the mixture to simmer for another 3 minutes to achieve the proper consistency. Remove from heat once done.
Incorporate White Chocolate: Add the white baking chips to the hot mixture. Cover the saucepan and let it rest for 3 to 4 minutes, allowing the chips to soften. Then stir until the white chips are completely melted and incorporated.
Add Marshmallow Fluff: Add the marshmallow fluff to the mixture and stir until completely incorporated. This adds extra creaminess and a smooth texture to your fudge.
Add Flavor and Color: Stir the prepared yellow food gel and banana extract mixture into the fudge. Continue stirring until the color is uniform throughout the fudge mixture.
Transfer to Dish: Use a silicone spatula or offset spatula to evenly spread the banana fudge into the prepared baking dish. For an extra touch, sprinkle the crushed Nilla wafers over the top of the fudge. Cover with aluminum foil.
Set and Chill: Allow the fudge to sit at room temperature for 30 minutes before transferring to the refrigerator to chill for at least four hours. Once the fudge is fully set, lift it out of the pan using the parchment paper. Use a large sharp knife to cut the fudge into five slices by five slices, yielding 25 pieces of fudge. Store in the refrigerator until ready to serve.