- Heat oven to 350 degrees. Grease and flour 2 9-inch cake pans and line bottoms with parchment paper.
- Whisk milk, egg whites, and vanilla together in medium bowl. In separate bowl whisk flour, sugar, baking powder, and salt together until combined.
- Transfer dry mix to stand mixer fitted with a paddle attachment, then add in butter slowly and mix until mixture resembles moist crumbs. Add all but ½ cup of milk mixture, then increase speed to medium and beat until pale and fluffy, about 2 minutes. Add remaining milk and beat for 20 seconds.
- Divide cake batter evenly into prepared cake pans and smooth tops with spatula. Bake for 23-25 minutes.
- Cool cakes in pan for 10 minutes, then invert onto greased wire rack. Let cool completely.
- Boil lemon juice, crème fraîche, salt, and ¾ cup sugar. Mix remaining sugar with cornstarch, then whisk together with egg yolks in bowl. Once lemon juice mixture has come to boil, pour half of mixture into egg yolks, whisking constantly.
- Pour egg mixture back in pot and bring back to simmer. Simmer for 4 minutes while whisking constantly. Transfer to bowl. Place plastic directly on top of lemon curd and set aside for 15 minutes.
- Remove plastic. Slowly add butter while whisking constantly until all butter has been used and there are no visible chunks, then transfer to plastic container, placing plastic directly on top and sealing with lid. Reserve in fridge until completely chilled.
- Whip heavy cream to stiff peaks. Reserve in fridge.
- Combine water and sugar in small pot and boil until it reaches 235 degrees (you can check using a standard candy thermometer). Meanwhile, place egg whites in stand mixer fitted with whisk attachment. Whisk egg whites until soft peaks form. Once formed add cream of tartar. Mix on medium speed until medium peaks form. While machine is still running, slowly drizzle in sugar mixture. Turn to high speed and whisk until cool.
- Once cooled, add whipped cream and mix to combine. Set aside until ready to use.
- Cut each cake into 2 even layers using large, serrated knife.
- Begin layering, starting with cake at bottom then followed by lemon curd.
- Repeat process until all cake layers have been used. Spread meringue on top of cake and slowly work your way down sides until completely covered with meringue.