LEMON MERINGUE PIE

Steps:

• Filling:
• Whisk sugar and cornstarch in a large saucepan to combine. Add eggs and egg yolks and whisk vigorously, making sure to get into corners of pan, until smooth and pale. Whisk in lemon zest and juice, salt, and 1½ cups water.
• Place saucepan over medium heat and bring to a simmer, whisking often and making sure to get into corners of pan, 8-10 minutes (mixture should be bubbling and thickened). Reduce heat and continue to simmer, whisking constantly, 3 minutes. Let cool 5 minutes, whisking every minute.
• Add butter to filling and whisk until melted and fully incorporated. Scrape filling into pie crust; smooth surface. Chill until cold and set, at least 2 hours and up to 3 days.
• Assembly:
• Combine egg whites, sugar, salt, and cream of tartar in the bowl of a stand mixer or another large heatproof bowl; set over a large saucepan filled with 1" simmering water (bowl shouldn't touch the water). Heat, stirring constantly, until sugar is dissolved and mixture is warm to the touch, about 4 minutes.
• Fit bowl onto mixer fitted with whisk attachment (or use an electric mixer) and beat on medium-high speed until meringue is more than tripled in volume and medium peaks form, about 4 minutes. Transfer to a piping bag fitted with a large round tip (or a resealable plastic bag will work-just snip off a corner after bag is filled). Pipe meringue over filling and toast with a kitchen torch or under the broiler.
• Do Ahead: Pie (without meringue) can be made 2 days ahead. Keep chilled.