"My great-grandmother would make one tray of this banana pudding every year, and you'd have to go on a scavenger hunt for it," says Kevin Gillespie. "I found it by accident four hours before anyone was supposed to, so I did the only thing an 8-year-old could do: I ate it all. This is the recipe I recreated from memory, and it's one of the best things you'll ever eat."
Custard base: Heat whole milk, half and half, vanilla, and vanilla bean in a large saucepan until bubbles start forming around the edge of the pan. Remove from heat and set aside. Place egg yolks and 2 cups of sugar into the bowl of a stand mixer and beat on high until light and fluffy, occasionally scraping down the sides of the bowl. Add the flour to the egg mixture on low just to incorporate. With the mixer on, slowly pour about a cup of the custard base from the saucepan into the egg mixture—this "tempering" will keep the eggs from cooking. Pour the tempered mixture through a fine mesh strainer into the saucepan (to smooth out any remaining lumps). Stir to combine, then fish out the vanilla bean. Split it open lengthwise, then use the back of a knife to scrape out the seeds. Return seeds and the scraped pod to the saucepan.
Heat the custard mixture over medium-high heat, stirring constantly with heat-resistant spatula until thickened. (If the custard turns lumpy, turn off the heat and whisk until it’s smooth again.) Whisk in salt and butter until smooth, then remove the vanilla bean pod and discard. To make it super-smooth, blend with an immersion blender until shiny. Set aside.
Assembly: Slice the pound cake into 1/2-inch-thick slices and set aside. Pour 1/3 of the custard into a casserole dish to cover the bottom. Add the cake in a single layer, breaking slices up so they all fit. Brush cake with coffee, then add half of the bananas. Press the ingredients down so they're even, then repeat with more custard, cake slices, coffee, and bananas, finishing with a final layer of custard.
Preheat oven to 375 degrees F. Put egg whites, remaining 1/2 cup sugar, and cream of tartar in the bowl of a stand mixer. Start the mixer on low (to avoid spatters), gradually raise speed to high to make sure the ingredients are combined, and then reduce to medium until soft peaks form. Spread meringue evenly over the banana pudding, then bake 5–6 minutes until the top is golden brown. Let cool several minutes, and serve warm.