Combine egg yolks, milk, lemon zest and lemon juice in a bowl. Mix thoroughly with a whisk
Pour this mixture into the pie crust
Preheat the oven to 325 F
Fill a 2-quart pot with enough water so that the bottom of a stainless steel Kitchen-Aid mixer bowl just touches the water. Bring the water to a simmer.
In a stainless steel Kitchen-Aid mixer bowl, whisk the sugar and egg whites until combined
Place the bowl with egg whites into the pot and continue to whisk until the mixture is hot, but not too hot to touch
Place the bowl with the egg white mixture in the mixer stand
Add the cream of tartar and whisk on medium-high until the meringue forms peaks that hold their shape, about 4 minutes
Place the meringue on top of the lemon-milk mixture in the pie crust
With a spoon or spatula spread the meringue out, making sure it goes all the way to the edge of the crust
Use the side of the spoon or spatula to make decorative peaks in the meringue
Bake for 20 minutes at 325 F