In a saucepan or double boiler, pour about 2 inches of water and bring to a simmer. The bowl should sit on top without touching the water.

In a bowl, combine lemon juice, eggs, egg yolks, sugar, and salt. Place the bowl on the saucepan and whisk continuously until the mixture thickens, about 10-12 minutes (or until it reaches 180°F).

Remove the bowl from the saucepan and cool until it reaches 140°F, stirring occasionally.

While the curd is cooling, cut the butter into 1-tablespoon cubes. Whisk in the butter one piece at a time until melted and fully incorporated.

Pour the curd into your baked pie crust and press plastic wrap onto the surface to prevent a skin from forming. Refrigerate for 3-4 hours or overnight until set.

Set up a double boiler by filling a pan with 2 inches of warm water and placing a bowl on top. The bowl should not touch the water.

Add egg whites, sugar, and cream of tartar to the bowl. Heat the mixture over low heat, stirring constantly until the sugar dissolves and the mixture is warm. Be careful not to cook the egg whites.

Once the sugar is dissolved, whip the egg whites on high until stiff peaks form. The mixture should be glossy and thick. Add the vanilla and mix to combine.

Spread the meringue over the chilled lemon curd. Toast with a blow torch or in the oven on broil for 1-3 minutes, watching closely to avoid burning.

Slice and serve. Store the pie in the refrigerator after topping.