How to make it:
Take all ingredients out of the fridge 1 hour before you start. Warm up milk to approx. 30°C / 86°F. Melt the butter. Whisk egg, egg yolks, salt, refined sugar, grated lemon zest, crumbled yeast, warm milk, and melted butter. Add flour to make a dough and knead until the dough doesn't stick to the bowl (use a food processor/dough hook if possible). Cover the bowl with a tea towel and prove for 1 hour at room temperature, until the dough has doubled in volume. Fold the dough and prove for another 10 minutes.
Remove the pits from the plums. Score the halved plums up to the middle and mix with ground cinnamon.
For the crumble, mix nut flour or ground almonds with flour, sugar, salt and butter.
Pre-heat your oven to 200°C / 400°F (fan). Put baking paper onto the baking tray. Roll the dough to a thickness of about 0.5 cm / 0.2 inch on a floured worktop. Put the dough on the baking tray and cover tightly with upright plums.
There are 2 variations for the crumble:
For immediate consumption: Sprinkle plum cake with butter crumble, turn down the oven heat to 160°C / 320°F (fan) and bake the cake for 35-40 minutes. Let cool down and dust with confectioner's sugar.
For keeping the crumble crisp for a longer time: Turn down the oven heat to 160°C / 320°F (fan) and bake the cake without the crumble. After 15 minutes, add crumble on a separate baking tray (on baking paper) and bake both for another 20 minutes, until the crumble is golden-brown. Take both trays out of the oven, heat up jelly or jam, coat the hot cake and then add crumble.
Tip: Enjoy your cake with a Viennese coffee or a glass of plum nectar.