• Preheat oven to 350F and butter and flour your 9" springform pan.

crumble topping

• First make the crumble topping. Put the softened 6 Tbsp unsalted butter, 3/4 cup flour and 3/4 cup sugar in a medium bowl and use your fingers to combine into a crumbly texture. Take the time to get all the butter evenly incorporated. Set aside.

cake

• Using a stand mixer or electric beaters cream the 3/4 cup granulated sugar, 1/2 cup salted butter , 1 tsp ground cardamom and 1/4 tsp ground mace or nutmeg until light and fluffy, about 3 minutes. Scrape down the bowl as necessary.
• Beat in the 2 large eggs , one at a time, scraping down the bowl after each one.
• Blend in the 1/4 cup sour cream or full fat yogurt and 1 tsp vanilla extract.
• With the mixer on low add the 1 tsp baking powder and then slowly add the 1 1/4 cups all-purpose flour until everything is incorporated. Finish mixing with a silicone spatula to scrape down the sides and bottom of the bowl. Turn into your prepared pan and spread out evenly.

plums

• Slice the plums and arrange over the cake batter to cover the surface completely. You can overlap them slightly. I like to start at the outer edge and work inwards. See photos for reference. Top with the crumble, using your fingers to press it together into larger crumbs as you add it.
• Slide into the oven and bake for about 50 minutes or until risen and slightly golden. A toothpick inserted in the center should come out with moist crumbs but no wet batter.
• Let the cake cool for about 10-15 minutes then carefully remove the springform pan sides, I like to run a thin knife around the edges to loosen first.