Make the plum compote: Put all the ingredients in a small saucepan and cook over medium heat, stirring frequently. The plums should start releasing juices.
Cook for around 10 minutes, until they're soft and at a point where you can use a masher to break them up. Remove the cinnamon stick and discard. Mash and stir together the plums until it's a somewhat uniform thick mixture (though it will still have chunks).
Make the pancake batter: Separate the eggs into two different medium bowls. Make sure the bowl with the egg whites is super clean (no greasiness).
Whisk the egg whites to soft peaks (not stiff peaks!). You can use a stand mixer or a hand mixer, I've found the latter easier for this amount of egg whites. Set aside.
In your other bowl, whisk the yolks with the 40g of sugar, milk, vanilla, and almond extract. Then add the flour and cinnamon and whisk to form a smooth batter. Gently fold the egg whites into the batter with a rubber spatula.
Cook the pancake: Melt half of the butter in a medium non-stick skillet (definitely nothing larger than a 10-inch) over medium heat.
Pour in the batter and cook for 2 to 4 minutes---start keeping an eye after 2 minutes, in case you have your heat up too high. You're looking for a strong golden underneath, a good crisp. It will still be super runny on top.
Then use a spatula to divide the pancake into quarters and flip each quarter over in the pan (don't worry if it tears, and yes, there will be a lot of batter spilling everywhere).
Once flipped, let it cook for a minute and then start roughly chopping it into smaller pieces. Keep stirring, chopping the pieces up until they start to solidify and form a crust. I have pics above on what it looks like at different stages.
As it's beginning to look cooked (not really any batter left), dot the remaining 15g of butter in small cubes over the cooking pieces and also sprinkle in the remaining sugar. Cook for another 1-2 minutes, turning and stirring occasionally, until the edges are golden and lightly caramelized.
Transfer to a plate and drizzle with plum compote and sprinkle with powdered sugar (just for pretty), and add whipped cream. Serve fresh and hot!