Whisk the lemon juice, granulated sugar, and egg yolks together in a medium saucepan until the mixture is uniform and smooth.
Set the saucepan over medium heat, then add the cubed unsalted butter.
Cook while stirring continuously, allowing the butter to melt completely as the lemon mixture gradually thickens.
Continue stirring for approximately 10–12 minutes, or until the curd is thick enough to coat the back of a spoon.
Remove the saucepan from the heat. Pour the lemon curd through a fine-mesh sieve into a clean bowl, pressing it through as necessary to eliminate any lumps.
Place plastic wrap directly against the surface of the curd to prevent a skin from developing.
Transfer the covered bowl to the refrigerator and chill until the curd is completely cold.
Combine the granulated sugar and water in a small saucepan.
Heat over medium-high heat until the sugar has dissolved and the syrup registers 240°F (115°C) on a candy thermometer.
While the syrup is heating, place the room-temperature egg whites in a clean mixing bowl. Beat with an electric mixer until soft peaks form.
With the mixer running at high speed, gradually pour the hot sugar syrup into the beaten egg whites in a slow, steady stream.
Continue beating until the meringue becomes thick, stiff, glossy, and cool when touched.
Beat for one additional minute when a firmer consistency is desired for piping.
Arrange small shooter glasses or individual dessert cups on a work surface.
Place a spoonful of finely crushed vanilla wafer cookies in the base of each glass.
Spoon or pipe a layer of the chilled lemon curd over the cookie crumbs.
Top the lemon curd with a spoonful or piped layer of Italian meringue.
Pass a kitchen torch lightly over the surface of each meringue topping until delicately browned.
Complete each shooter with a small amount of freshly grated lemon zest for fragrance, color, and fresh citrus flavor.
Serve the lemon meringue pie shooters immediately for the best contrast of textures, or refrigerate them until serving time.