The rye makes the base drier and sharper, so the fruit keeps its own sweetness. Coarse crumble on top, which crisps up in the oven rather than disappearing into it.
Most plum cakes are too sweet. Not because of the fruit — damsons bring plenty of acidity of their own — but because of the base. A classic shortcrust of wheat flour and a lot of sugar competes with the fruit instead of carrying it.
Rye flour turns that around. It is drier, slightly earthy, and lets the fruit keep the leading role. The crumble comes from the same dough, just with a little more butter, so the whole cake tastes like one thing rather than two things stacked on each other.
For a 26 cm springform tin or a small tray. Tastes better on the second day than the first.
Mix both flours, sugar, salt and cinnamon. Add the cold cubed butter and rub it in with your fingertips into coarse crumbs.
Do not work it too long — the butter should stay cold.
Set aside about a third of the crumbs for the topping. Add the egg to the rest and press quickly together into a dough. Wrap and chill for 30 minutes.
Heat the oven to 180 °C conventional. Press the dough into the greased tin, pulling a small rim up the side. Scatter the breadcrumbs over the base — they soak up the juice from the fruit.
Set the plums tightly on the base, slightly overlapping, cut side up.
Better too much fruit than too little. It collapses in the oven.
Scatter the reserved crumbs over the top. Bake 50 minutes, until the crumble is golden and the juice bubbles at the edges.
Cool in the tin. Warm, the base falls apart; cold, it holds together.
If the base turns soggy, there were too few breadcrumbs. They are not filler — they are the only protection against the plum juice.
