Preheat the oven to 350°F / 175°C. Butter the springform and line the bottom with parchment; lightly grease the parchment.

Halve and pit 450–500 g plums. If you like, toss them with 1–2 tsp sugar and a pinch of cinnamon; set aside.

In a bowl whisk together: 130 g all-purpose flour, 70 g rye flour, 1½ tsp baking powder, ¼ tsp baking soda, ¼ tsp salt, ½ tsp ground cinnamon, ½ tsp ground cardamom, 1/8 tsp ground cloves, 1/8 tsp ground nutmeg. Stir to evenly distribute the spices.

In your mixer (or with a hand mixer), cream 150 g softened butter with 150 g coconut or maple sugar until light and slightly fluffy — ~2–3 minutes. Add the zest of 1 orange and mix briefly.

Add the 3 large eggs, one at a time, beating until each is incorporated and scraping the bowl sides between additions.

Fold in 120 g sour cream (or Greek yogurt) until combined.

Add the dry mix to the butter-egg mixture in two additions, folding gently with a spatula until just incorporated. Don’t overmix — you want a tender crumb. (If you want ground nuts for depth, fold in 40–60 g finely ground hazelnuts or almonds now.)

Spread the batter evenly into the prepared springform, smoothing the top with an offset spatula.

Arrange the plum halves on top, cut side up, in concentric circles or a pretty pattern. Press each plum gently into the batter so it sits partially embedded — they’ll sink a little while baking.

Bake at 350°F / 175°C for about 40–50 minutes. Start checking at 40 minutes: a skewer inserted into the cake (between plums) should come out mostly clean with a few moist crumbs, not raw batter. If the top is browning too fast, tent loosely with foil after ~25–30 minutes.

Remove from oven and cool on a rack for 15–20 minutes. Release the springform and transfer to the rack to cool further. If you want a glaze, whisk ½ cup (60 g) powdered sugar with 1–2 tsp fresh orange juice until pourable and drizzle while the cake is slightly warm. Or simply dust with powdered sugar.

Serve slightly warm or at room temperature — lovely with a dollop of crème fraîche, whipped cream, or a scoop of vanilla ice cream. Store covered at room temperature for 1–2 days, or refrigerate up to 4 days. Rewarm slices briefly in a low oven for that just-baked feel.