Great-grandma Martha baked this 4 ingredient miracle whenever times were tough and somehow it tastes exactly like sunshine.

Because this pie was born in the Depression era, the spirit of the recipe is to keep it simple and work with what you have. If you’d like a slightly softer tang, you can reduce the apple cider vinegar to 3 tablespoons and add 1 tablespoon of water to keep the liquid balance similar. For a slightly firmer custard, bake closer to the 45-minute mark and chill thoroughly before slicing. If you’re not strictly limiting yourself to four ingredients, a pinch of salt and a splash of vanilla extract deepen the flavor without changing the character of the pie. A dusting of cinnamon or nutmeg over the top before baking gives it a more “apple pie–like” aroma, which some families remember from their grandmothers’ versions. For a sturdier crust, you can blind-bake the pie shell for 8 to 10 minutes at 375°F (190°C), then cool slightly before adding the filling; this is especially helpful if your pie plate is very thick or your oven runs cool. Food safety notes: Because the filling is egg-based, be sure to bake the pie until the custard reaches a safe temperature—look for a mostly set center with only a slight jiggle, and avoid serving if the middle is still liquid. Always cool the pie on the counter for no more than 2 hours, then refrigerate any leftovers promptly. Keep the pie covered in the refrigerator and discard if it has been left out at room temperature for more than 2 hours after baking or serving.