Po’ Boys & Pickles on Forest Avenue has long been one of my go-to places when I need something fast for dinner but don’t want fast food.

For a long time I used to order the same thing – a fried shrimp po’boy – before branching up. I saw the list of milkshakes on the chalkboard but always resisted the temptation. Then one day I decided to splurge, but instead of the salted caramel or the chai shake, I went for the plain Jane vanilla custard. I’m not sure why. But what happened next was one of the weirdest, yet most pure food experiences I’ve ever had.

Not to be saccharine about it, but it was one of those Proust-madeleine-“Remembrance of Things Past” moments, where a taste unlocks something in your brain and you are flooded with memories. This simple vanilla custard shake, which owner Peter Zinn tells me is made from scratch with real vanilla beans, in an instant shot me back more than four decades to my grandmother’s kitchen at the holidays, when her refrigerator always contained a glass jug filled with homemade boiled custard, made especially for my father, who loved it so much he’d have downed the whole gallon if my mother hadn’t stopped him.

Boiled custard is a southern version of eggnog, a “drinking custard” without all the fuss of nutmeg and (in the Bible belt, anyway) booze. It’s made mainly during the Christmas holidays, but also has a long tradition of comforting ailing Southern folks in their sick beds. It’s simple to make, just a handful of ingredients – eggs, sugar, milk and vanilla – whisked together in a double boiler, but you have to be patient. Despite the name, you shouldn’t let the milk boil, so it has to be heated slowly or the eggs will scramble. And it’s best served chilled, so it needs time in the fridge.

When we visited my grandparents during the holidays, my father, brother and I would make a beeline for the refrigerator to check for boiled custard. If my grandmother made it while we were there, I remember being surprised by how such simple ingredients could be transformed into something so delicious. It tastes like drinking melted vanilla ice cream.

Sometime between my childhood and middle age, big dairies in the South caught on and started putting their own cartons of boiled custard in the dairy case, right next to the cartons of eggnog, in November and December. They typically contain corn syrup and other things that ruin the purity of the experience. (Ironically, one of the companies that produces this is called Purity.) My brother is approaching 60 but turns into a little boy at the mere mention of this drink, which is so decadent we allow ourselves to partake only at Christmas. He is the boiled custard police, monitoring our consumption and announcing when we need another boiled custard run now that my grandmother is no longer alive to make it.

Back to Po’ Boys & Pickles. I’m sure it must be the all-natural ingredients, but when I took my first sip of the restaurant’s vanilla custard shake, there was no question that, as Proust says, “an exquisite pleasure had invaded my senses.” It’s not exactly like my grandmother’s boiled custard – the texture isn’t quite the same – but it’s close enough. I was immediately in the old farm kitchen, celebrating a cold Tennessee Christmas with family.

How lovely to know that I can now have that experience year-round, without having to get out the double boiler.