Polish plum kefir crumb cake

By Nik, founder of 東歐嚴選｜kefir.link and former chef · Updated 2 November 2026

Purple plums sink softly into a tender, golden cake, and a layer of buttery crumble crackles on top. This is the kind of plain sheet cake Polish families bake when the orchards fill with fruit, to serve in squares with afternoon coffee or tea. Milk kefir gives the crumb a gentle tang and keeps it soft long after the cake has cooled.

When Polish orchards fill with plums

In Poland, plums hang heavy in the orchards from midsummer to the end of autumn, and the smell of plum cake baking is one of the first signs of fall. The classic versions are raised with yeast or built on shortcrust, while this quick one is stirred with a spoon. The usual plum is the węgierka, an egg-shaped fruit with thick purple skin and firm yellow flesh. Elsewhere, look for prune plums or other firm purple plums, ripe but not soft, because overripe, spongy fruit floods the cake with juice.

Keeping the crumb light under juicy fruit

Kefir and oil keep the cake moist, so it does not dry out early. Stir the dry ingredients in only until no flour shows, because extra mixing builds gluten and turns the crumb dense and tough. Cold eggs and kefir can leave a damp, underbaked layer at the bottom, so let them come to room temperature first. Wet or crowded fruit has the same effect, so dry the plums well after washing, keep to the amount given, and toss very juicy ones in a little flour. Keep the oven door closed for the first 20 to 30 minutes, since a sudden drop in temperature can make the cake sink.

Cardamom, walnuts and a spoonful of cream

A pinch of cinnamon or cardamom in the batter suits plums well, and oats and walnuts can go into the crumble. Frozen plums can go straight onto the batter without thawing; allow 5 to 10 minutes more baking. Serve the squares plain, or with whipped cream, sour cream, plain yogurt or a scoop of vanilla ice cream.