Preheat the oven to 350 degrees Farenheit. Line a 9 x 13 inch pan with parchment paper, and then lightly grease it as well. Set aside.

Make the meringue: Add 3 egg whites and 1/4 tsp kosher salt to a clean medium bowl, or to the bowl of a stand mixer with the whisk attachment. I generally use a medium mixing bowl and a handheld electric mixer. 

Begin beating the egg whites on low speed, until they are slightly thickened and a more cohesive texture, instead of some thicker and some thinner bits like they are when you first crack an egg.

Increase the mixer to medium speed and gradually add in 3/4 cup of granulated sugar, beating for several seconds in between each addition. When all the sugar is added, the mixture should be white, foamy and thickened.

Add vanilla extract and continue to beat on medium-high speed for several more minutes, until the egg whites are thick, glossy and holding stiff peaks. Set this bowl aside while you prep the cake batter.

Make the cake batter: In a small bowl, whisk together your flour, salt, and baking powder. Set aside.

In a large mixing bowl (or the bowl of a stand mixer, this time with the paddle attachment), beat the softened butter and the other 3/4 cup of white sugar on medium speed until light and fluffy, about 2-3 minutes.

Add the egg yolks and beat again until fully combined, scraping down the sides of the bowl if needed. Add buttermilk and beat again on low speed- it's okay if it doesn't look totally cohesive. Add the dry ingredients and beat until fully combined. It will be a thick batter texture. 

Bake the cake: Scrape all of the yellow cake batter into the prepared pan. Use an offset spatula to evenly spread the batter out over the pan. 

Using a spatula, gently add all of the meringue mixture on top of the cake batter. Clean off your offset spatula and use it to gently spread the meringue in an even layer on top of the cake layer.

Bake the cake for 20-30 minutes, until the cake is cooked through and a toothpick comes out clean, and the meringue layer is lightly browned-it will probably also be cracked in a couple spots and very puffy. It will settle and continue to set as the cake cools. I do find that if I stop baking while the meringue is still very white, it is not always totally set in the middle when it cools. Plus I really love when the meringue gets a tiny bit crispy!

Let the cake cool in the pan for 5-10 minutes, then use the parchment paper to gently lift the entire cake out to a cooling rack to cool completely.

Prep whipped cream & berries: Wash and cut your strawberries and add them to a medium bowl along with lemon juice and 1 Tbsp granulated sugar and mix well. Set aside, if you like them juicy leave them for 15 minutes or so before adding them to the cake.

To a larger mixing bowl add 1 Tbsp granulated sugar, vanilla extract, mascarpone, and heavy cream. Use a handheld electric mixer to beat on medium-high speed until soft peaks form. 

Assemble the Cake: Don't assemble the cake before it's fully cooled!

Cut the cooled cake in half and transfer one half to a cake plate or baking sheet, whatever you wish to use. Add half of the whipped cream to the top and gently spread it. Top the whipped cream with half of the berries. Gently place the other half of the cake on top, then repeat with the remaining whipped cream and berries. 

Enjoy!