Topping (Plum Layer)

3 tbsp unsalted butter, softened

⅓ cup brown sugar, packed

4–5 fresh plums, pitted and thinly sliced (enough to cover an 8-inch pan)

Cake

6 tbsp unsalted butter, at room temperature

⅓ cup light brown sugar, packed

1 large egg, at room temperature

1 tsp pure vanilla extract

½ cup sour cream, at room temperature (full-fat recommended)

1 cup all-purpose flour

½ tsp baking soda

½ tsp ground cinnamon

½ tsp ground cardamom (optional)

¼ tsp ground ginger (optional)

¼ tsp sea salt

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Preheat oven to 350°F (175°C). Grease an 8-inch round cake pan and line the bottom with parchment.
In a small bowl, mash softened butter and brown sugar for the topping into a spreadable paste. Spread evenly over the parchment-lined bottom of the pan.
Arrange plum slices in slightly overlapping concentric circles to cover the surface.
In a medium bowl, whisk together flour, baking soda, cinnamon, cardamom, ginger, and sea salt.
In a large bowl, beat 6 tbsp butter and ⅓ cup brown sugar until light and fluffy, 2–3 minutes.
Beat in the egg, then mix in vanilla.
Stir in sour cream until combined.
Add dry ingredients to the wet mixture and stir just until no dry streaks remain; do not overmix.
Dollop batter over plums and gently spread to edges.
Bake 35–45 minutes, until golden and a toothpick inserted in the center comes out clean or with a few moist crumbs.
Cool in pan for 10–15 minutes, run a knife around edges, place a serving plate on top, and invert. Remove pan and peel away parchment.
Cool at least 15 more minutes before slicing.

Use firm, ripe plums for best texture and color.

Line pan with parchment to ensure topping releases cleanly.

For a different fruit profile, swap in peaches, nectarines, or apricots.

Check doneness early when using a 9-inch pan, as baking time may be shorter.