Once your jam and pastry cream are chilled, you can start making the pancakes for the cake.
Combine the flour, sugar, and salt in a large bowl.
Add half of the milk and whisk until you have a completely smooth, non-lumpy batter.
In a separate bowl, combine eggs and remaining milk; whisk well to combine.
Add the eggs mixture to the rest of the batter and whisk until smooth.
Whisk in the melted butter, making sure it gets fully incorporated.
You should be left with a smooth batter with no lumps that is relatively thin.
To cook the pancakes, use a non-stick pan (our pan is a 9 inch pan on the bottom) over medium heat. Scoop up about 1/3 cup of the batter and pour into the center of the pan, while simultaneously twisting the pan in a circle so that the batter coats the bottom of the pan all the way to the edges.
Flip after a minute or two and cook for another 30 seconds on the second side. Set aside onto a plate. Repeat this until you run out of batter and let the pancakes cool. We ended up with 24-28 pancakes - this will depend on the size of your pan, how thick you make them, or how many you end up snacking on during the cooking process!
To assemble the cake, start with a pancake on the bottom.
Add a thin layer of pastry cream over the pancake, spreading it with an offset spatula or a butter knife.
Add another pancake, then spread on a thin layer of jam.
Repeat with alternating layers of jam and pastry cream, until you run out of pancakes, filling, or both! We found that we got just the right amount of pastry cream and jam for 24 pancake layers (so 12 layers of each filling). You may have a few pancakes leftover!
Remember to keep the layers of filling thin so that you have enough filling for the entire cake!
For decoration: make whipped cream by whipping heavy cream, sugar, and vanilla together in stand mixer or using a handheld mixer or just a whisk, until it reaches stiff peaks.
To decorate, we added the whipped cream on top and some sprinkles, but you can leave it bare or make it even fancier if you like with fresh fruit, chocolate, crumbled up cookies, or anything else you'd like!
This cake is best after chilling for an hour or two, as it helps to set up the layers! If you serve it right away, be prepared that some of the layers may slide around a little bit! Enjoy!