In a medium sauce pot, whisk collectively the granulated sugar, cornstarch and salt till no clumps stay. Add within the egg yolks, water, and lemon juice and whisk till mixed. Prepare dinner the combination over medium warmth, stirring continually, till combination thickens and begins to boil, about 10 minutes. Boil for 1 minute, stirring continually, then take away from the warmth and add within the butter and lemon zest, stirring till mixed. Pour the custard into the ready pie crust.
For the meringue: In a really clear and dry bowl of a stand mixer, mix the egg whites and cream of tartar collectively on HIGH velocity with the whisk attachment, simply till foamy. Step by step add within the sugar, about one Tablespoon at a time, beating till the combination kinds stiff peaks, about 2-4 minutes. Add within the vanilla and beat properly.
Unfold the meringue rapidly over the lemon custard, sealing the custard below a layer of meringue. Pop the pie into the oven and bake for 20-25 minutes, watching intently so the meringue does not burn. It needs to be gentle golden brown and toasted. Cool fully at room temperature, then refrigerate for at the very least 3-4 hours to set earlier than serving.