Line an 8×8-inch (20×20 cm) baking pan with parchment paper, letting it hang over the sides to create a sling. Lightly spray the parchment with nonstick spray if your parchment tends to stick.

Add about an inch of water to a small saucepan and bring it to a low simmer. Place a heat-safe bowl on top, making sure the bottom of the bowl does not touch the water. Alternatively, you can use a microwave-safe bowl to melt the mixture in the microwave.

Add the white chocolate chips, sweetened condensed milk, and butter pieces to the heat-safe bowl. Stir slowly and often with a rubber spatula until the chocolate is almost fully melted and the mixture looks glossy and thick. If using a microwave, heat in 20–30 second bursts, stirring well after each burst, until nearly melted and smooth.

Remove the bowl from the heat (or from the microwave). Quickly stir in the instant banana cream pudding mix, crushed freeze-dried bananas, vanilla extract, and fine sea salt until evenly combined. If the mixture seems too thick or slightly grainy, add heavy cream 1 tablespoon at a time, stirring until the fudge becomes smooth and spreadable.

The fudge mixture should be thick but spreadable, similar to warm peanut butter. If it runs like a sauce, keep stirring off the heat for a minute or two so it can cool and firm up. If it is very stiff and hard to spread, warm it gently and add a tiny splash more cream until it loosens slightly.

If using vanilla wafer cookies, fold about half of the crushed wafers into the fudge mixture for added crunch and classic banana cream pie flavor. Reserve the remaining wafers for topping.

Pour the fudge mixture into the prepared pan. Use a spatula to spread it evenly into the corners. Tap the pan firmly on the counter a few times to help release any air bubbles.

Sprinkle the remaining crushed vanilla wafers evenly over the top of the fudge and press them very gently so that they adhere to the surface.

Cover the pan loosely and refrigerate for at least 2 hours, or until the fudge is firm enough to slice cleanly. For the neatest squares, chill for 3–4 hours or overnight.

Use the parchment sling to lift the fudge out of the pan and transfer it to a cutting board. With a sharp knife, cut into approximately 1-inch squares, wiping the knife with a warm, damp cloth between cuts. Serve slightly chilled or closer to room temperature, as preferred.

Arrange the banana cream fudge squares on a serving plate, pack them into tins for gifting, or tuck a few pieces into lunchboxes. They’re also excellent alongside a cup of coffee or tea.