Part 1: Making the Luscious Homemade Custard

1. Combine Dry Ingredients: In a medium, heavy-bottomed saucepan, whisk together ¾ cup of granulated sugar, ⅓ cup of all-purpose flour, and ¼ teaspoon of salt. This prevents lumps when you add the liquid.
2. Prepare Egg Yolks: In a separate small bowl, lightly whisk the 3 large egg yolks.
3. Gradually Add Milk: Slowly pour the 2 ½ cups of whole milk into the saucepan with the dry ingredients, whisking constantly until smooth and fully combined.
4. Cook the Custard: Place the saucepan over medium heat. Cook, stirring constantly and scraping the bottom and corners of the pan with a heatproof spatula or whisk to prevent scorching and lumps. Bring the mixture to a gentle boil. Continue to cook and stir for 1-2 minutes more, or until the custard has noticeably thickened to a pudding-like consistency. It should coat the back of a spoon.
5. Temper the Egg Yolks: This is a crucial step to prevent the yolks from scrambling. Remove the saucepan from the heat. Very slowly, pour about ½ cup of the hot milk mixture into the whisked egg yolks, whisking the yolks vigorously as you pour. This gently warms the yolks.
6. Combine and Finish Cooking: Pour the tempered egg yolk mixture back into the saucepan with the remaining milk mixture. Return the saucepan to medium heat. Cook, stirring constantly, for another 2-3 minutes, until the custard is thick, bubbly around the edges, and has reached at least 160°F (71°C) on an instant-read thermometer. Do not overboil.
7. Add Flavor and Richness: Remove the saucepan from the heat. Stir in the 2 tablespoons of unsalted butter (cut into pieces) and 1 ½ teaspoons of pure vanilla extract until the butter is melted and the custard is smooth and glossy.
8. Cool Slightly (Optional but Recommended): To prevent the custard from cooking the bananas too much upon assembly, you can let it cool for about 10-15 minutes, stirring occasionally to prevent a skin from forming. Alternatively, press plastic wrap directly onto the surface of the custard while it cools.

Part 2: Assembling the Banana Pudding

1. Prepare Your Dish: Choose a 2 to 2.5-quart baking dish (an 8×8 inch or 9×9 inch square dish, or a similar sized oval/round dish works well) or a glass trifle bowl for a beautiful presentation.
2. First Layer of Wafers: Arrange a single layer of Nilla Wafers to cover the bottom of your chosen dish. You can break some wafers to fill in any gaps.
3. First Layer of Bananas: Top the wafers with a single layer of sliced bananas. Try to cover the wafers as evenly as possible.
4. First Layer of Custard: Pour about one-third of the warm (or slightly cooled) custard evenly over the bananas and wafers. Gently spread with a spatula if needed.
5. Repeat Layers: Create another layer of Nilla Wafers, followed by another layer of sliced bananas, and then another third of the custard.
6. Final Layers: Add a final layer of Nilla Wafers. Top with the remaining sliced bananas (if you have any left and want extra banana flavor, otherwise end with wafers before the final custard). Pour the remaining custard over the top, ensuring all wafers and bananas are covered. You might reserve a few whole wafers or crushed wafers for garnish if not making meringue.

Part 3: The Crowning Glory – Making the Meringue (If Using)

If you’re skipping the meringue, you can cover the pudding with plastic wrap (let it cool a bit first if still very hot) and refrigerate. Serve chilled, perhaps with a dollop of fresh whipped cream.

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Beat Egg Whites: In a very clean, grease-free bowl (glass or metal is best), beat the 3 large room-temperature egg whites and ¼ teaspoon of cream of tartar with an electric mixer on medium-high speed until soft peaks form. Soft peaks will droop over when you lift the beaters.
3. Gradually Add Sugar: With the mixer still running, gradually add the 6 tablespoons of granulated sugar, one tablespoon at a time, beating well after each addition. Continue to beat until the meringue is stiff, glossy, and the sugar is completely dissolved. (Test by rubbing a bit between your fingers; it should feel smooth, not gritty).
4. Add Vanilla: Beat in the ½ teaspoon of pure vanilla extract until just combined.
5. Spread Meringue: Immediately spread the meringue evenly over the top of the warm banana pudding, ensuring it touches the edges of the dish all the way around. This helps prevent the meringue from shrinking. Create decorative swirls and peaks with the back of a spoon or a spatula.
6. Bake: Bake in the preheated 350°F (175°C) oven for 10-15 minutes, or until the meringue is lightly golden brown on the peaks. Keep a close eye on it, as meringue can brown quickly.
7. Cool and Chill: Remove the banana pudding from the oven. Let it cool on a wire rack at room temperature for at least 1 hour. Then, cover loosely with plastic wrap (try not to let it touch the meringue) and refrigerate for at least 4-6 hours, or preferably overnight, before serving. Chilling allows the flavors to meld and the pudding to set properly.