Make apricot jam ahead of time (even the day before!) by combining apricots, sugar, a pinch of salt, and vanilla paste in a small pot.
Heat over medium heat, stirring often, until the apricots start to release their juices.
Once bubbling, lower the stove temperature to low and stir frequently. The jam should cook for around 15-20 minutes until thickened; the apricots should be totally broken down. Remove from the heat and place in a separate container to let cool, transferring to the fridge to fully cool down.
Prepare Danish pastry cream (kagecreme) at least one hour in advance of preparing the cake; you can also make this the day before! It needs to be fully chilled in the fridge prior to use - you can use an ice bath to cool it down faster if necessary. Preheat oven to 220F (105C).
Make the meringue by combining egg whites and a splash of lemon juice in the bowl of a stand mixer (or a large mixing bowl if using a handheld mixer!).
Whisk together until the egg whites begin to look frothy.
Add sugar slowly one tablespoon at a time, waiting in between additions until the sugar has dissolved. You will probably have to stop the mixer to scrape down any sugar that sticks to the sides. Add in vanilla extract.
Once all the sugar has been added, keep whisking for at least a few more minutes or until you reach stiff peaks (dip the whisk attachment into the mixture, then pull it straight up and turn it upside down - the meringue should have a point and not flop over!). This could take a little while longer! Keep scraping down the sides and continuing to whisk as needed.
Line two baking sheets with parchment paper. Once the meringue is ready, divide the mixture into three piles - two on one sheet, and the last one on the second baking sheet.
Spread the meringue into round disks, around 7-8" in diameter (19-20cm).
Bake for an hour; turn off the oven and let the meringue layers cool for at least 15 minutes in the oven. Then crack the oven open to let the meringues cool down for another 30 minutes. Remove from the oven and let cool completely. This process helps keep the meringues from cracking and collapsing so they don't immediately break when we assemble the cake.
While the layers are cooling, make the whipped cream by adding heavy cream and vanilla extract to a stand mixer or mixing bowl. We don't sweeten our whipped cream for this recipe because the meringue is so sweet, but if you want to, add some sugar as well! Using the whisk attachment or a whisk, whip the cream until it reaches stiff peaks.
Please note: If you want a more structural cake, you do not have to add whipped cream to the pastry cream, just use the pastry cream on its own, and use about ⅓ the amount of whipping cream to make whipped cream for decorating.
Remove about one third of the whipped cream from the bowl (for decorating the top).
Add the totally chilled pastry cream to the bowl of the stand mixer with the whipped cream, and whisk until it comes together.
Fold a few times with a spatula to make sure the pastry cream and whipped cream is totally incorporated. Now you've made a creme diplomat!
Before decorating, slice 2-3 apricots and place in a bowl with a few tbsp of sugar. Let sit and stir occasionally - it should turn syrupy.
Now it's assembly time! Place one layer of meringue first, then spread a thick layer of the creme diplomat over the top, all the way to the edges. You'll need to divide the creme diplomat between two layers and a little bit extra for the top; so we usually add a little less than half to the first layer. Then, add a layer of apricot jam over the top and spread to the edges. About 3-4 tbsp should suffice.
Repeat with a disk of meringue, creme diplomat (again, a little less than half of the total amount), and apricot jam (3-4 tbsp).
Place the final disk of meringue on top.
If you have any remaining creme diplomat, spread it over the top.
Layer on apricots, whipped cream, and any additional jam you would like to make a beautiful topping for the cake.
This is a cake best enjoyed immediately! The slices will be messy to cut if you press on the cake too hard, so try your best to cut carefully with a sharp knife without too much pressure. Worst case, you can serve in a bowl (seriously, if everything falls apart, put it all in a bowl and call it a trifle). Chilling for about 10-15 minutes can also help the layers set up a bit better, but too long in the fridge and the meringue will get soggy and you risk collapse.
Enjoy and store any leftovers in the fridge!