For the filling
While the pie crust is cooling, make the lemon cream. Bring about 2 inches of water to a simmer in a medium saucepan.

In a stainless steel bowl, whisk together all of the ingredients for the filling, except the butter. Place the bowl over the simmering water being careful not to let the bowl touch the water. Continue to whisk the mixture constantly until the mixture registers between 160 and 180 degrees, until your mixture is nice and thick.

Let the mixture cool to 140 degrees or about 5 minutes, stirring occasionally to release heat. With an immersion blender or conventional blender, blend in the butter, one tablespoon at a time, waiting to add the next until the first has been blended in completely.

Let the cream cool to room temperature.

For the Italian meringue
Bring the sugar and water to a boil in a small saucepan. Brush the sides down with a wet pastry brush to avoid any crystals from forming. Boil until syrup register 238 on a candy thermometer (this will take less time than you think!).

Beat the egg whites in the bowl of an electric mixer fitted with the whisk attachment on low speed until foamy.
Add cream of tartar and salt. Raise the speed to medium; mix until soft peaks form. If you reach this stage before the syrup is done, continue to mix on low speed until the syrup is done. Do not stop mixing or the egg whites will start to lose their shape.

With the mixer running on medium-low, slowly pour the hot syrup down the side of the mixing bowl, without touching the whisk. Mix on medium-high speed until stiff, glossy peaks form and mixture has cooled, about 5-7 minutes.

Assembling the pie
Pour the lemon cream into the pie crust. Top with meringue and spread to the edges of the crust, covering all of the cream.

With the back of a spoon, make peaks for decoration.With a small kitchen torch, toast the meringue to your desired aesthetic.

Slice, serve and enjoy immensely.