Heat the oven to 350°F before preparing the filling. Starting with a fully heated oven helps the foam begin browning as soon as the pie goes in.

Thaw the pie shell following its package directions while you make the custard. The shell should be flexible enough to hold the filling without cracking around the rim.

Combine the 6 egg yolks, condensed milk, warm evaporated milk, vanilla extract, and salt in a large bowl. Stir until the mixture looks uniform and glossy, with no thick ribbons of condensed milk remaining.

Gently fold the stiff egg whites into the yolk mixture. Stop once the filling looks foamy, since vigorous stirring can knock the air out of the whites.

Pour the mixture through a fine-mesh sieve into the pie shell, then lift only the collected foam from the sieve and spread it over the surface. Discard the thicker bits left behind so the custard bakes with a smooth, even texture.

Set the pie on a baking sheet and bake at 350°F for 15 minutes, then reduce the oven to 325°F and bake for 30 to 45 minutes, rotating the baking sheet halfway through. The top should turn dark brown, the edges should feel set when the pan is nudged, and the center should retain a small gelatin-like wobble.

Cool the pie completely before cutting, then chill it if you prefer cold slices. The custard will settle as it cools, and a little gentle deflation across the surface is normal.