Begin by warming 3 cups of whole milk in a saucepan over medium heat. Keep an eye on it; you want it hot but not boiling. In another bowl, mix the egg yolks and sugar until the sugar is dissolved. Gradually whisk in the flour, followed by the hot milk, creating a smooth mixture. Next, return this mixture to the saucepan over medium heat. Stir continuously until it thickens, about 10 minutes. When it gets to a pudding-like consistency, remove from heat and stir in the butter, vanilla extract, and salt. Let this cool while you prepare the rest.

Now, take out a trifle dish or a deep glass bowl. Lay a layer of vanilla wafers at the bottom, followed by a layer of sliced bananas. Next, pour a third of your cooled custard over the bananas and wafers. Repeat this process until you run out of ingredients, finishing with a layer of custard on top.

In a clean bowl, beat the egg whites until soft peaks form. Gradually add sugar and the cream of tartar while beating, until you reach stiff peaks. Spread this meringue over the custard layer, making sure to seal the edges to prevent it from shrinking while baking.

Preheat your oven to 350°F (175°C). Bake your pudding for about 10 to 15 minutes, or until the meringue is golden brown. Keep an eye on it to avoid burning. Once it reaches that lovely golden color, remove it from the oven.

Let the pudding cool to room temperature, then refrigerate for at least a couple of hours before serving. This helps the flavors meld beautifully.