Preheat the oven to 375º F (180º C). Grease and line a rectangular cake pan of about 15 x 13 inches (38 x 33 cm) with parchment paper.
In a medium bowl, sift together the flour, salt and baking powder.
In a big bowl with an alectric mixer, cream together the butter and sugar for 4 minutes until you get a lighter in color and fluffier mixture.
Beat in the vanilla extract and keep beating until fully integrated. Add in the egg yolks one by one, beating for 30 seconds after each addition.
Add in the flour mixture in three separte additions alternating with the milk, beating after each addition. Beat for 1 more minute until you get a smooth batter.
Pour the mixture in the cake pan, even it out, and put it aside while you make the meringue.
For the meringue and baking:
In a big bowl put the egg whites with the salt and beat with an electric mixer for 2 minutes until soft peaks form.
Add in the sugar in three additions along with the vanilla extract, beating for 1 minute after each addition until firm peaks form and you get a shiny fluffy meringue.
Carfully pour the meringue on top of the cake batter already in the cake pan and spread it all over. Add the sliced almonds on top.
Bake at 375º F (180º C ) for 30 to 35 minutes until the cake turn slightly golden brown and the maringue has grown a little.
Once the cake is ready, take it out of the oven and put it on a cooling rack to cool down completely. Then cut it in half lengthwise to get two pieces of abour 7.5 x 6.3 inches (19 x 16 cm).
For the filling and to assemble:
Using a sharp knife, open up the vanilla bean lenghtwise and carefully scrape out the seeds in it.
In a pot over medium heat on the stove put the milk along with half the sugar and the vanilla bean seeds. Let it cook for 2 minutes, without it boiling, mixing occacionally with a whisk.
Meanwhile, in a small bowl, mix the rest of the sugar with the salt, egg yolks, corn starch and flour with a fork. Add in a little of the milk mixture and beat for this egg yolk mixture to temper.
Pour the egg mixture into the pot with the milk mixture and cook over low medium heat for 4 minutes aproximately, whisking non-stop until a thick cream forms. It is really important not to stop beating and doing it carefully for the cream to be smooth.
Take the cream off the heat, add in the vanilla and beat until it is fully incorporated. Pour the cream in a different clean bowl, then cover it with plastic kitchen wrap (it must touch the cream surface for it not to form a curd or crust) and refrigerate for 30 minutes.
Meanwhile, put the whipping cream in a big bowl and beat using the electric mixer for 3 to 4 minutes until soft peaks form (it is important not to overbeat).
Once the cream has refrigerated, incorporate the cream in three separate additions using a rubber spatula, mixing from the outside in for the mixture not to deflate.
Put one of the pieces of cake with the meringue side facing down on a big plate (where the cake will be presented).
Add in the filling and spread until you even it out. Then place the other half of the cake with the meringue side facing up and you´re done. Refrigerate for at least 30 minutes before cutting and serve with some strawberries or any type of berries if you want to.