Step 1
Line the base and sides of a 20cm round cake tin with baking paper. Preheat the oven to 175C fan-forced (195C conventional).
Step 2
To make the sugar crust, combine the ingredients in a small bowl and mix to the consistency of wet sand. Set aside.
Step 3
Sift the flour, baking powder, baking soda and salt into a medium bowl, then set aside.
Step 4
Place the butter and sugar in the bowl of an electric mixer and beat with the paddle attachment on medium-high speed until the mixture’s light and creamy (about 2 minutes).
Step 5
Add the eggs one at a time, beating well after each addition. Using a flexible spatula, scrape the base and sides of the bowl, as well as the paddle, and continue to beat for a few more seconds.
Step 6
Add the vanilla, then, on low speed, alternately add the sifted dry ingredients and sour cream in 2-3 batches. Scrape down the base and sides of the bowl to make sure the batter is evenly mixed, then transfer to the prepared cake tin.
Step 7
Arrange the sliced plums on the batter without overlapping, then scatter the sandy cardamom sugar all over. Place the cake in the oven and bake for about 50 minutes or until a skewer inserted into the middle comes out clean. Transfer to a wire rack to cool for at least 30 minutes before removing from the tin.
Step 8
Dust the top of the cake lightly with icing sugar and serve with the extra sour cream.
